Rear-projection screen and rear-projection image display

ABSTRACT

A rear-projection screen  3,  including at least a lenticular lens sheet  32  and a Fresnel lens sheet  31,  is configured so that the lenticular lens sheet  32  contains, in a base material thereof made of a resin, light diffusing microparticles made of a resin having a refractive index different from a refractive index of the base material, and the light diffusing microparticles satisfy 0.5 μm≦ΔN 1 ×d 1 ≦0.9 μm, where ΔN 1  represents a difference between a refractive index of the light diffusing microparticles and a refractive index of the base material of the lenticular lens sheet, and d 1  represents an average particle diameter of the light diffusing microparticles. With this, a rear-projection screen with small wavelength dependency of diffusion characteristics can be provided utilizing only resins with general properties.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] Both of Aspects I and II of the present invention relates to arear-projection screen and a rear-projection display (rear-projectionimage display device) in which the rear-projection screen is used.

[0003] 2. Related Background Art

[0004] Aspect I of the Present Invention

[0005] Needs for large screens have grown, mainly in the field oftelevision picture tubes recently, and rear-projection displays havegained a spotlight as suitable for such a large screen. Generally, a CRTis used as an image source for the rear-projection display. Further, atype in which a spatial modulation element such as a liquid crystalelement is used for advantages of lightness and compactness has beenproposed and drawn attention.

[0006] First of all, the following description will depict a type inwhich a CRT is used as an image source. FIG. 6 is a view schematicallyillustrating the basic configuration of the same.

[0007] In this display, images are formed by single-color CRTs 1 (1R,1G, and 1B) for the three main colors, respectively, and are enlargedand projected by projection lenses 2 (2R, 2G, and 2B) corresponding tothe same, respectively, so as to be superimposed on a screen 3. Here,the reference codes R, G, and B correspond to red, green, and blue,respectively. As shown in the figure, light that is divergent from thecenter to the periphery and that partially has a sharp directivity isincident on the screen 3 disposed at the image formation plane. Besides,red, green, and blue lights incident on respective parts have anglesdiffering from each other, respectively. The screen 3 is required toarrange such projected lights appropriately so as to allow good imagerecognition.

[0008] Minimum image observation is enabled by using a simple lightdiffusing sheet as the screen 3. Since the projected light is incidentthereto divergently as described above, however, light at the peripheralpart has outward directivity since the projected light is incidentdivergently thereon. Therefore, the brightness of the screen isremarkably uneven. For instance, the screen has an extremely lowluminance at the periphery as compared with a luminance at the centerwhen observed from the front, and has a high luminance at an end closerto the observer and a low luminance at an end farther from the observerwhen observed diagonally.

[0009] To avoid such unevenness, generally a Fresnel lens sheet 31 isprovided on a light-projected side of a diffusing sheet. The Fresnellens sheet 31 functions to convert the projected light divergentlyincident from the projection lenses 2 on the screen 3 into substantiallyparallel rays. By this function, green projected light is converted intoparallel rays perpendicular to the screen surface, while blue and redprojected lights are converted into parallel rays that are verticallyparallel with each other and that have certain set angles, respectively,with respect to the normal line of the screen surface in any horizontalplane. In the case where the projected light simply is diffused in thisstate, the green projected light leaves the screen symmetrically withrespect to the normal direction of the screen surface, while the red andblue projected lights leave the screen asymmetrically, thereby causingcolors of the screen to change depending on the viewing direction. Thisphenomenon is called “color shade” and degrades the image quality.

[0010] To cope with this, a lenticular lens sheet 32 that has a specialconfiguration having black stripes (BS) and pairs of lenticular lenses(this configuration is hereinafter referred to as “BSPaired-Lenticular-Lens Structure”) is used so as to diffuse projectedlight with a sharp directivity so as to make the same observable atvarious angles, and to suppress color shift. The function thereof isdepicted with reference to FIG. 7.

[0011]FIG. 7 illustrates a cross section of the lenticular lens sheet 32in the horizontal direction, and ray trajectories of green projectedlight and red projected light are indicated with a solid line (G) and abroken line (R), respectively. As shown in the figure,light-incident-side lenticular lenses 321 and light-exiting sidelenticular lenses 322 that are paired are provided so that the lenses ofeach pair share the same optical axis. By doing so, an exiting angle ofthe red light that has been incident diagonally is corrected so thatdiffusion symmetric to the normal direction of the screen is realized,as is with the green light, whereby the color shift is suppressed.Furthermore, because light passes through limited portions of thelight-exiting surface due to the light collecting function of thelight-incident-side lenticular lens 321, it is possible to provide lightabsorbing layers 323 at light non-transmission portions of thelight-exiting surface. Since the light absorbing layers are black incolor and are provided in a stripe form, they are called black stripes,abbreviated as BS, and function significantly to reduce the diffusingreflection of external light incident on the screen in a brightenvironment, thereby improving the contrast.

[0012] It should be noted that generally the lenticular lens is formedso that its lengthwise direction is directed in the vertical direction,and the refraction by the lenticular lens affects only in the horizontaldirection, and does not contribute to diffusion in the verticaldirection. Therefore, light diffusing microparticles made of a materialhaving a refractive index different from that of a base are dispersedinside the lenticular lens sheet so that light is diffused in thevertical direction. At interfaces between the base and the lightdiffusing microparticles, light rays are refracted depending on arefractive index difference Δn according to the Snell's law, therebybeing diffused isotropically. This refracting function is more intenseas the difference between the refractive index of the base and that ofthe light diffusing microparticles is greater, which means that light isdiffused more as the difference between the refractive index of the baseand that of the light diffusing microparticles is greater.

[0013] Generally, a material tends to have a greater refractive index ata shorter wavelength, and this is called the wavelength dispersion ofthe refractive index, which is represented by an Abbe constant νd. Thedispersion increases and the Abbe constant νd decreases as a materialhas a higher refractive index. The relationship between the refractiveindex nd of a typical material as an optical resin material and the Abbeconstant νd is shown in Table 1 and FIG. 10. TABLE 1 POPULAR NAME,REFRACTIVE ABBE MATERIAL TRADE NAME INDEX nd CONSTANT vd PMMA Acryl1.492 57.6 Polystyrene Styrol 1.590 30.9 Polycarbonate PC 1.585 29.9Allyl Glycol CR39 1.504 57.8 Carbonate Copolymer Zeron ® 1.533 42.4Styrene Methacrylate Copolymer Lustran ® 1.569 35.7 StyreneAcrylonitryle Polymethyl TPS ® 1.466 56.4 Pentane

[0014] Thus, in order that a base and light diffusing microparticles aremade of materials selected from generally-used transparent resinmaterials so that they have a refractive index difference Δntherebetween, unavoidably a high-refractive-index high-dispersionmaterial and a low-refractive-index low-dispersion material arecombined. Consequently, the refractive index difference Δn also is madewavelength-dependent, and hence, the refractive index difference Δntends to increase as the wavelength is shorter.

[0015] In the case where the combination of the light diffusingmicroparticles and the base is such a combination of general materials,the refractive index difference Δn increases as the wavelength isshorter, thereby leading to significant diffusion. As a result, thediffusion exhibits a wavelength-dependency such that the diffusion ofblue light having a shorter wavelength exceeds the diffusion of redlight having a longer wavelength.

[0016] As the base material of the lenticular lens sheets, a transparentresin is used, for instance, polymethyl methacrylate (PMMA) with arefractive index of approximately 1.49, or an MS resin (copolymer ofstyrene and methyl methacrylate (MMA)) with a refractive index ofapproximately 1.52. In such a case, beads, each in a pearl form, made ofan MS resin with a refractive index that is approximately 0.02 to 0.07greater than that of the base material, are used often. The refractiveindex of the MS resin material used for the base material and the lightdiffusing microparticles can be adjusted by adjusting a mix proportionof MMA and styrene. Since the refractive index of MMA is approximately1.49 and the refractive index of styrene is approximately 1.59, therefractive index of the MS resin can be adjusted in a range of 1.49 to1.59. The wavelength dispersion of the MS resin increases as therefractive index nd increases (the Abbe constant νd decreases as therefractive index nd increases), and this agrees with the correlationline shown in FIG. 10.

[0017] In the case where the lenticular lenses are made of materialsarranged as above, the refractive index difference Δn between the baseand the light diffusing microparticles is made wavelength-dependent forthe aforementioned reasons. Therefore, the refractive index differenceΔn increases, thereby resulting in significant diffusion, as thewavelength is shorter. Consequently, the diffusion is madewavelength-dependent, for instance, the diffusion of blue light having ashort wavelength is more significant than the diffusion of red lighthaving a long wavelength. Since light with a sharp directivity isincident on a rear-projection screen in particular, a remarkable colorvariation takes place in which the screen is reddish when observed fromthe front and becomes more bluish as the observation angle increases (asobserved more diagonally). It should be noted that in the case of arear-projection screen including lenticular lens sheets, the colorvariation is remarkable in the vertical direction, since the diffusionin the horizontal direction is achieved by the refracting function ofthe lenticular lenses.

[0018] The color variation depending on the observation angle stems froma cause different from that of the color shift due to the horizontalarrangement of the image sources of the three principal colors, andcannot be suppressed by the aforementioned BS Paired-Lenticular-LensStructure.

[0019] Another configuration of the rear-projection screen is, as shownin FIG. 8, a configuration in which the light diffusing microparticlesare not dispersed inside the lenticular lens sheet 32 but a lightdiffusing sheet 33 is provided on the image-observed side of thelenticular lens sheet 32. This configuration reduces optical loss thatis caused by the diffusion of light inside the lenticular lens sheet 32and the incidence of the same on the black stripes, thereby improvingthe efficiency and suppressing the color shift in the horizontaldirection.

[0020] In this configuration also, the above-described color variationin the vertical direction due to the wavelength characteristics of thelight diffusing microparticles dispersed in the light diffusing sheet 33and the resin material used for the base tends to occur, as in the casewhere the light diffusing microparticles are dispersed inside thelenticular lens sheet.

[0021] Furthermore, in the type in which light from a lamp 4 ismodulated by using a spatial modulation element 5 like a liquid crystalpanel as an image source as schematically illustrated in FIG. 9, asingle projection lens 6 is used for image projection by superimposingthree principal-color images before the projection lens 6. Therefore,the aforementioned color shift correction is unnecessary. In this case,it also is proposed to use a sheet that is obtained by bonding atransparent lenticular lens sheet 34 and a light diffusing sheet 33 witheach other with a transparent adhesive. The transparent lenticular lenssheet 34 has a flat light-exiting surface and is provided with blackstripes (BS) on its light non-transmission portions on the light-exitingsurface. In this configuration, the external light incident on the lightdiffusing sheet 33 is absorbed by the black stripes effectively beforebeing diffused and reflected on its rear surface. Therefore, thecontrast in a bright environment is improved.

[0022] In this configuration, the color shift in the horizontaldirection does not take place, but the drawback of the color variationin the vertical direction that tends to occur when a common resinmaterial is used still remains unsolved.

[0023] As a measure for reducing the wavelength dependency of thediffusion, a technique of combining plural kinds of light diffusingmicroparticles that cancel their respective wavelength dependencies ofthe diffusion characteristics, has been proposed; the light diffusingmicroparticles are, for instance, “light diffusing microparticles of ahigher refractive index and high dispersion than those of the base, andlight diffusing microparticles of a higher refractive index and lowerdispersion than those of the base” (JP11(1999)-338057A). This techniqueallows the overall wavelength dependency of the diffusion to besuppressed, thereby realizing a configuration characterized in that thecolor variation depending on the observation angle is small.

[0024] The rear-projection screen sometimes is configured so that lightdiffusing microparticles are dispersed in a transparent base, not inorder to secure an angle of visibility as described above, but in orderto reduce the glaring of the screen, which is called scintillation. Thescintillation is remarkable particularly in the type as shown in FIG. 9in which the spatial modulation element 5 such as a liquid crystal panelis used. The reason for this is as follows: the projected light reachingthe screen 3 has a particularly sharp directivity, because themagnification is high due to the small size of the image source ascompared with the CRT projection type, and hence the projection lens 6used therein has a great F number. In this case, the light diffusingmicroparticles are dispersed in the Fresnel lens sheet 31. By using thistype, it is possible to reduce speckle or scintillation.

[0025] As disclosed by JP11(1999)-338057A, the use of plural kinds oflight diffusing microparticles that cancel the respective dispersionwavelength-dependencies decreases the dispersion wavelength-dependencyof the light diffusing sheet. In this case, however, as a material forone of the kinds of the light diffusing microparticles, a material of ahigher refractive index and lower dispersion than those of the base isneeded. In the case where resins are used as the base and the lightdiffusing microparticle material, polycarbonate or the like, apart fromMMA and styrene, may be used as a transparent material applicable for anoptical purpose. These resin materials, however, tend to exhibit higherdispersion as the refractive index is higher, and hence, theaforementioned combination is infeasible.

[0026] To obtain the aforementioned combination, there is no practicalalternative other than the use of a transparent glass material of ahigher refractive index and lower dispersion than those of a resin forforming a light diffusing microparticles of a higher refractive indexand lower dispersion than those of a resin base. However, in the casewhere a light diffusing sheet or a rear-projection screen is producedusing the light diffusing microparticles made of a glass material,damage to a cutting edge upon cutting the sheet or screen increases ascompared with the case where light diffusing microparticles made of aresin material are used. Besides, there is a problem of a highermanufacturing cost as compared with the case where generally-usedresin-made light diffusing microparticles are used.

[0027] In the case where light diffusing microparticles are dispersed ina Fresnel lens sheet to reduce scintillation, side effects such as theimpairment of the resolving power and the decrease in the efficiency areproduced. The impairment of a resolving power is caused when lightdiffused at one point in the Fresnel lens sheet spreads by the time itreaches the lenticular lens sheet, then again is diffused by thelenticular lens sheet. The resolving power decreases in proportion to adiffusing characteristic rendered to the Fresnel lens sheet and adistance between two diffusing elements. On the other hand, theefficiency is impaired because components lost to absorption by BSprovided on the light-exiting surface of the lenticular lens sheetincrease due to diffusion at the Fresnel lens sheet. The decrease in theefficiency becomes more remarkable as the diffusion at the Fresnel lenssheet becomes more significant.

[0028] Aspect II of the Present Invention

[0029] Needs for large screens have grown mainly in the field oftelevision picture tubes recently, and rear-projection displays havegained a spotlight as suitable for such a large screen. Generally, a CRTis used as an image source for the rear-projection display, but a devicemaking use of light modulation by a liquid crystal panel or the like hasbeen developed and is expected to realize further lightness andcompactness. A basic configuration of the same is shown schematically inFIG. 16.

[0030] Light emitted from a lamp 4 is subjected to spatial modulation bythe liquid crystal panel 5 so that an image is formed, and the image isenlarged and projected by a projection lens 6. It should be noted thatan actual device generally is provided with three liquid crystal panelsto obtain color display, and in this case, the device has a complexstructure including a color separation optical system for separating thelight from the lamp 4 into red, green and blue components, a colorsynthesizing optical system for synthesizing lights that has passedthrough the three liquid crystal panels, and the like. However, theseare omitted herein.

[0031] Furthermore, examples of similar types making use of spatialmodulation include a type utilizing a reflective liquid crystal elementas a modulating element, and a type utilizing a multiplicity ofmicromirrors whose angles are variable (micromirror device).

[0032] Light that is divergent from the center to the periphery and thatpartially has a sharp directivity is incident on the rear-projectionscreen 3 disposed at the image formation plane. The degree of thedirectivity is represented by a projection directivity angle θ, which isexpressed as:

θ=tan⁻¹[1/{2×F×(M+1)}]≈1/{2×F×(M+1)}

[0033] where M represents a projection magnifying power M and Frepresents an F number of the projection lens.

[0034] It should be acknowledged that in a device utilizing a CRT as animage source, the projection magnifying power M for a display with adiagonal of the 50-inch order is approximately 10 since a CRT with anabout 5-inch diagonal is used, and the F number is set as small asapproximately 1 so that diffused light from a fluorescent body iscaptured. Consequently, a projection directivity angle θ ofapproximately 0.05 (about 3°) is obtained.

[0035] On the other hand, in a type utilizing an image modulatingelement such as a liquid crystal panel, the F number of the projectionlens is as great as 3 since an element with a diagonal of approximately1 inch is used and illuminating light with a relatively high directivityneeds to be used in view of the characteristics of the element.Therefore, the projection directivity angle θ is as small asapproximately 0.003 (about 0.2°), and projected light incident on thescreen has an extremely strong directivity.

[0036] The screen 3 functions to arrange such projected lightappropriately so as to enable good image recognition.

[0037] Even in the case where a simple diffusing means (diffusing plate)is used as the screen 3, the minimum image observation is enabled.However, since the projected light is incident divergently as describedabove, the light has an outward directivity at the peripheral part,thereby causing remarkable unevenness in the brightness of the screen.For instance, the screen 3 has an extremely low luminance at theperiphery as compared with a luminance at the center when observed fromthe front, and it has a high luminance at an end closer to the observerand a low luminance at an end farther from the observer when observeddiagonally.

[0038] To avoid such unevenness, generally a Fresnel lens sheet 35 isprovided on a light-projected side of a diffusing means.

[0039] The Fresnel lens sheet 35 functions to convert the projectedlight divergently incident from the projection lens 6 on the screen 3into parallel rays with a principal directivity that is substantiallyperpendicular to the screen surface.

[0040] Thus, if the light is diffused after having been converted intolight with a principal directivity perpendicular to the screen surfaceat any part of the screen, it is possible to obtain substantiallyuniform brightness throughout the whole screen, irrespective of thedirection in which the screen is viewed.

[0041] Furthermore, generally a laminated lenticular lens sheet 36 isused as the diffusing means, instead of a simple isotropic diffusingplate.

[0042] Considering the observation range, the image recognition atvarious angles need to be achieved as to the observation range in thehorizontal direction, whereas the image recognition only in the standingstate and in the sitting state suffices as to the observation range inthe vertical direction. Therefore, it is possible to provide an evenlybright image by effectively allocating light to necessary regions byanisotropic diffusion. The laminated lenticular lens sheet 36 providesthe anisotropic diffusion.

[0043] The laminated lenticular lens sheet 36 is composed of a BS (blackstripe)—provided lenticular lens film 362, and a diffusing sheet 361obtained by integrally providing a light diffusing layer 3612 and atransparent layer 3611. As shown in FIG. 17, the lenticular lens film362 has lenticular lenses 3621 provided on a light-incident-side surfacethereof whose lengthwise direction is directed in the verticaldirection. The lenticular lens film 362 has a thickness set so that thefocus position of each lenticular lens 3621 substantially coincides withthe light-exiting surface of the film. Therefore, the projected lightincident on the lenticular lens film 362 is converged in the vicinity ofthe light-exiting surface, and then, exits therefrom. On thelight-exiting surface of the lenticular lens film 362, lightnon-transmission regions that the projected light does not pass throughand whose lengthwise direction is directed in the vertical direction areprovided in a stripe form. On the light non-transmission regions, lightabsorbing layers (black stripes: BS) 3622 are provided in a stripe form.The light-exiting surface of the BS-provided lenticular lens film 362and the diffusing-layer-3612-side surface of the diffusing sheet 361 aremade to adhere to each other with a transparent adhesive or atransparent bonding material 363.

[0044] As shown in FIG. 17, an array pitch P1 of the lenticular lenses3621 on the lenticular lens film 362 preferably is as small as possibleso that the moire effect caused by the lenses and the pixels issuppressed and that a high resolving power is obtained. In order todecrease the pitch P1, it is necessary to decrease the pitch at whichthe black stripes 3622 are provided on the light non-transmissionregions on the light-exiting surface of the lenticular lens film.Conventionally it has been difficult to provide the black stripesprecisely at a fine pitch on the light non-transmission regions. Now,however, a technique of selective exposure by making use of the lightcollecting function of the lenticular lenses has been developed, so thata fine pitch at a level of not more than 0.2 mm is obtained. In thiscase, the lenticular lens film 362 has a thickness t1 of not more than0.3 mm so as to obtain a diffusion angle required of the lenticular lensfilm 362 and to collect light onto the light-exiting surface.

[0045] The diffusing sheet 361 is made of, as a base, a transparentmaterial such as polymethyl methacrylate (PMMA), or an MS resin(copolymer of styrene (refractive index: 1.59) and methyl methacrylate(MMA, refractive index: 1.49)), and only in the diffusing layer 3612part in the diffusing sheet 361, the light diffusing microparticleshaving a refractive index slightly greater than the refractive index ofthe transparent material forming the foregoing base are dispersed. Thethickness of the diffusing sheet 361 generally is about 2 mm so as toobtain a mechanical strength that allows the whole laminated lenticularlens sheet 36 to be maintained stably, while the thickness of thediffusing layer 3612 and the thickness of the transparent layer 3611 areset to about 0.1 mm to 0.2 mm, and about 1.0 mm to 1.8 mm, respectively.

[0046] It should be noted that it is possible to obtain an identicaldiffusing function by not making the diffusing sheet in a two-layerstructure, but dispersing the diffusing material throughout thethickness thereof of approximately 2 mm. This, however, is inferior tothe above-described two-layer structure with respect to the resolvingpower, and particularly in the case where a great diffusioncharacteristic is imparted so that the angle of visibility is increased,significant deterioration of the resolving power tends to occur.

[0047] With the configuration as above, the projected light that hasbeen converted by the Fresnel lens sheet 35 into substantially parallellight is diffused to a relatively wide range in the horizontal directionby the synergism of the refractive effect of the lenticular lenses 3621and the light diffusing microparticles in the diffusing layer 3612,while it is diffused in a relatively narrow range in the verticaldirection only by the effect of the light diffusing microparticles inthe diffusing layer 3612. Thus, the aforementioned anisotropic diffusionis realized.

[0048] As to the rear-projection display in which a light modulationelement as described above is used, a phenomenon called scintillationhas emerged, which was not apparent in a device utilizing a CRT as animage source. The scintillation is a phenomenon in which glaring occurson a screen due to minute light and dark patterns, and it also is calledspeckle.

[0049] The reason why scintillation particularly becomes apparent in therear-projection display utilizing a light modulation element is that thedirectivity of the projected light incident on the screen issignificantly more intense as compared with that of a display utilizinga CRT as described above, thereby producing high spatial coherence thatleads to mutual interference of light diffused by the light diffusingmicroparticles.

[0050] JP8(1996)-313865A proposes, as a technique for suppressingscintillation, to provide two layers of diffusing elements with acertain set distance therebetween. In this case, generally, thelaminated lenticular lens sheet in which generally the light diffusingmicroparticles are dispersed is utilized as the diffusing element, andin addition to that, the Fresnel lens sheet 35, which is a basic elementof the screen like the laminated lenticular lens sheet, is utilized alsoas the diffusing element.

[0051] In JP10(1998)-293361A and JP10(1998)-293362A, an appropriatediffusion characteristic to be imparted to the Fresnel lens sheet isdefined with a haze value.

[0052] Thus, the dispersion of the light diffusing microparticles notonly in the laminated lenticular lens sheet 36 but also in the Fresnellens sheet 35 makes it possible to suppress scintillation. At the sametime, however, it produces unfavorable side effects as a rear-projectiondisplay.

[0053] One of the side effects is as follows: among the light diffusedby the Fresnel lens sheet 35, components incident on the laminatedlenticular lens sheet 36 at relatively great angles are absorbed by theblack stripes 3622 provided on the lenticular lens film 362, therebybeing lost.

[0054] Scintillation is suppressed more effectively as the diffusioncharacteristic imparted to the Fresnel lens sheet 35 increases, but theaforementioned absorption loss increases as the diffusion characteristicincreases.

[0055] Another side effect is a drawback in that the resolving powersignificantly deteriorates when a gap is produced between the Fresnellens sheet 35 and the laminated lenticular lens sheet 36.

[0056] The Fresnel lens sheet 35 and the laminated lenticular lens sheet36 tend to warp in response to changes in the ambient temperature andmoisture, since they usually are made of a resin. A technique ofpreviously making the both warped so as to cause the same to adhereclosely and fixing the peripheral part of the same is available toprevent a gap from being produced between the Fresnel lens sheet 35 andthe laminated lenticular lens sheet 36 due to such environmentalchanges. With the use of such a technique, however, it still isdifficult to completely prevent such a gap from being produced underreadily conceivable environmental changes.

[0057] Furthermore, in the case where the laminated lenticular lenssheet 36 and the Fresnel lens sheet 35 are thus warped previously, thescreen surface is warped in a state of being mounted on the device. Insuch a state, the projection magnifying power varies depending on aposition, and such a projection magnifying power distribution causes aprojected image to be deformed. Besides, the reflection image ofexternal light also is caused to have deformation, which makes anundesirable appearance, particularly when the device is turned off.

SUMMARY OF THE INVENTION

[0058] Aspect I of the Present Invention

[0059] Therefore, with the foregoing in mind, it is a first object ofthe aspect I of the present invention to provide a rear-projectionscreen with small wavelength dependency of diffusion characteristics,which can utilize resin materials with general properties, with theaforementioned problems being solved.

[0060] It is a second object of the aspect I of the present invention toprovide a rear-projection screen in which scintillation is suppressedwhile the side effects caused by the diffusion by the Fresnel lens sheetare suppressed.

[0061] It also is a still another object of the aspect I of the presentinvention to provide a rear-projection display in which the foregoingrear-projection screen is used.

[0062] To achieve the foregoing first object, in a rear-projectionscreen according to the aspect I of the present invention, lightdiffusing microparticles dispersed inside as a diffusing element arearranged so that the product of a refractive index difference Δn fromthe base material and an average particle diameter d, that is, Δn×d, isin a range of 0.5 to 0.9. This makes it unnecessary to use lightdiffusing microparticles made of a material with specificcharacteristics, for instance, a higher refractive index and highdispersion than those of the base material, or a higher refractive indexand lower dispersion than those of the base material. This allows lightdiffusing microparticles made of a general resin material to be used forachieving diffusion characteristics with small wavelength dependency.

[0063] Furthermore, to achieve the foregoing second object, in arear-projection screen according to the aspect I of the presentinvention, light diffusion by light diffusing microparticles dispersedin a Fresnel lens sheet is made smaller than light diffusion by lightdiffusing microparticles dispersed in a light diffusing sheet or alenticular lens sheet, and the light diffusing microparticles dispersedin the Fresnel lens sheet are arranged so that the aforementioned Δn×dis in a range of 0.1 to 0.3. This allows scintillation to be suppressedeffectively, while reducing side effects such as a decrease in theresolving power, optical loss, etc.

[0064] Furthermore, since a rear-projection display according to theaspect I of the present invention is provided with the rear-projectionscreen according to the aspect I of the present invention, an imagedisplay that undergoes a minimum of color tone variation depending on anobservation direction, exhibits a minimum of scintillation and excels inresolution can be achieved.

[0065] Aspect II of the Present Invention

[0066] It is an object of the aspect II of the present invention toprovide a rear-projection screen in which the aforementioned problemsare solved, scintillation is minimized, loss due to absorption by blackstripes is reduced, and a resolving power is not significantly impairedin response to ambient changes, and also to provide a rear-projectiondisplay in which the foregoing rear-projection screen is used.

[0067] To achieve the foregoing object, a rear-projection display and arear-projection screen according to the aspect II of the presentinvention are configured so that a diffusing layer provided in alaminated lenticular lens sheet is positioned apart from a focal planeof a lenticular lens sheet and in a predetermined range that iseffective for suppressing scintillation and reducing a decrease in theresolving power. Furthermore, preferably a transparent Fresnel lenssheet containing substantially no diffusing material is used.

[0068] More specifically, a first rear-projection display according tothe aspect II of the present invention includes a spatial modulationelement, and a rear-projection screen on whose surface on alight-projected side an image formed by the spatial modulation elementis projected so that the image is observed from an image-observed sideopposite to the light-projected side. In the rear-projection display,the rear-projection screen includes a first screen element forconverting projected light from the spatial modulation element intosubstantially parallel light, and a second screen element for diffusingthe substantially parallel light. The second screen element includes alenticular lens array that is provided on the surface on thelight-projected side and whose lengthwise direction is directed in avertical direction, a diffusing layer provided on the image-observedside to the lenticular lens array, and a transparent layer providedbetween the lenticular lens array and the diffusing layer. In this, adistance t1 between a light-projected-side surface of the diffusinglayer and a focal plane of the lenticular lens array satisfies FormulaII-1 below, and a distance t2 between an image-observed-side surface ofthe diffusing layer and the focal plane of the lenticular lens arraysatisfies Formula II-2 below:

t 1≧f 1  Formula II-1

t 2≦f 1×Pg/P 1  Formula II-2

[0069] where f1 represents a distance between a valley of the lenticularlens array and the focal plane, Pg represents a pixel pitch on thescreen, and P1 represents an array pitch of the lenticular lens array.

[0070] With the foregoing first rear-projection display, scintillationcan be reduced by satisfying Formula II-1, and a high resolving powercan be obtained by satisfying Formula II-2.

[0071] Furthermore, a second rear-projection display according to theaspect II of the present invention may be configured so that thedistance t2 between an image-observed-side surface of the diffusinglayer and the focal plane of the lenticular lens array satisfies FormulaII-3 below, in place of Formula II-2 for the first rear-projectiondisplay:

t 2≦Pg/2/tan(γi)  Formula II-3

[0072] where γi represents an in-layer equivalent angle in thetransparent layer that is obtained by converting an observation angle γat which a luminance of {fraction (1/10)} of that in a normal directionis obtained due to diffusion caused by the diffusing layer, and isexpressed as Formula II-4 below:

γi=a sin(sin(γ)/n)  Formula II-4

[0073] where n represents a refractive index of the transparent layer.

[0074] With the foregoing second rear-projection display, scintillationcan be reduced by satisfying Formula II-1, and a high resolving powercan be obtained by satisfying Formula II-3.

[0075] Next, a first rear-projection screen according to the aspect IIof the present invention is a rear-projection screen on whose surface ona light-projected side an image formed by a spatial modulation elementis projected so that the image is observed from an image-observed sideopposite to the light-projected side. The rear-projection screenincludes a first screen element for converting projected light from thespatial modulation element into substantially parallel light, and asecond screen element for diffusing the substantially parallel light.The second screen element includes a lenticular lens array that isprovided on the surface on the light-projected side and whoselength-wise direction is directed in a vertical direction, a diffusinglayer provided at the image-observed side of the lenticular lens array,and a transparent layer provided between the lenticular lens array andthe diffusing layer. In this, a distance t1 between alight-projected-side surface of the diffusing layer and a focal plane ofthe lenticular lens array satisfies Formula II-1 below, and a distancet2 between an image-observed-side surface of the diffusing layer and thefocal plane of the lenticular lens array satisfies Formula II-5 below:

t 1≧f 1  Formula II-1

t 2≦f 1×P 1×0.7  Formula II-5

[0076] where f1 represents a distance between a valley of the lenticularlens array and the focal plane, and P1 represents an array pitch of thelenticular lens array, the unit of t1 is according to that of f1, andthe unit of t2 is millimeters.

[0077] With the foregoing first rear-projection screen, scintillationcan be reduced by satisfying Formula II-1, and a high resolving powercan be obtained by satisfying Formula II-5.

[0078] Furthermore, a second rear-projection screen according to theaspect II of the present invention may be configured so that thedistance t2 between an image-observed-side surface of the diffusinglayer and the focal plane of the lenticular lens array satisfies FormulaII-6 below, in place of Formula II-5 for the first rear-projectionscreen:

t 2≦0.35/tan(γi)  Formula II-6

[0079] where f1 represents a distance between a valley of the lenticularlens array and the focal plane, and γi represents an in-layer equivalentangle in the transparent layer that is obtained by converting anobservation angle γ at which a luminance of {fraction (1/10)} of that ina normal direction is obtained due to diffusion caused by the diffusinglayer, and is expressed as Formula II-7 below:

γi=a sin(sin(γ)/n)  Formula II-7

[0080] where n represents a refractive index n of the transparent layer,and the unit of t1 is according to that of f1, and the unit of t2 ismillimeters.

[0081] With the foregoing second rear-projection screen, scintillationcan be reduced by satisfying Formula II-1, and a high resolving powercan be obtained by satisfying Formula II-6.

BRIEF DESCRIPTION OF THE DRAWINGS

[0082]FIG. 1 is a graph showing the relationship between an observationangle of a light diffusing sheet and a color temperature.

[0083]FIG. 2 is a graph showing the relationship between an observationangle of a light diffusing sheet and a relative luminance.

[0084]FIG. 3 is a graph showing the relationship between a product of arefractive index difference and a particle diameter as to a lightdiffusing sheet and color temperature shift.

[0085]FIG. 4 is a perspective view illustrating a rear-projectiondisplay according to one embodiment of the aspect I of the presentinvention.

[0086]FIG. 5 is a perspective view of a rear-projection displayaccording to another embodiment of the aspect I of the presentinvention.

[0087]FIG. 6 is a view illustrating a state of a rear-projection screenaccording to one embodiment of the aspect I of the present inventionwhen used in a three-tube-type rear-projection display.

[0088]FIG. 7 is a partly enlarged cross-sectional view of a BSpaired-lenticular-lens sheet.

[0089]FIG. 8 is a view illustrating a state of a rear-projection screenaccording to another embodiment of the aspect I of the present inventionwhen used in a three-tube-type rear-projection display.

[0090]FIG. 9 is a view illustrating a state of a rear-projection screenaccording to still another embodiment of the aspect I of the presentinvention when used in a rear-projection display of the spatialmodulation type.

[0091]FIG. 10 is a graph showing the relationship between a refractiveindex of a typical optical resin material and the Abbe constant.

[0092]FIG. 11 is a view schematically illustrating a cross section inthe horizontal direction of a rear-projection display according to oneembodiment of the aspect II of the present invention.

[0093]FIG. 12 is a view illustrating a cross section in the horizontaldirection of a principal part of a laminated lenticular lens sheetcomposing a rear-projection screen according to the aspect II of thepresent invention.

[0094]FIG. 13 is a cross sectional view in the horizontal direction forexplaining the range of a beam spot in the case of a rear-projectiondisplay according to one embodiment of the aspect II of the presentinvention.

[0095]FIG. 14 is a cross sectional view in the horizontal direction forexplaining the range of a beam spot in the case of a rear-projectiondisplay according to one embodiment of the aspect II of the presentinvention.

[0096]FIGS. 15A and 15B are views for explaining a modulation degreeaccording to the range of a beam spot in the case of the rear-projectiondisplay according to one embodiment of the aspect II of the presentinvention.

[0097]FIG. 16 is a cross-sectional view in the horizontal directionschematically illustrating a configuration of a conventionalrear-projection display.

[0098]FIG. 17 is a cross-sectional view in the horizontal directionillustrating a principal part of a laminated lenticular lens sheetcomposing a conventional rear-projection screen.

DETAILED DESCRIPTION OF THE INVENTION

[0099] Aspect I of the Present Invention

[0100] First of all, before describing each embodiment, the followingdescription will depict matters that the present invention relies on.The inventors of the present invention produced screens, using samplesof light diffusing sheets in which light diffusing microparticles withvarious refractive indices and various particle diameters were used, andmounted each screen on a rear-projection display so as to examine indetail the characteristics of the screens. Consequently, the inventorsfound that even in the case where a kind of light diffusingmicroparticles made of a material whose refractive index wavelengthdispersion is different from that of a base is used alone, thewavelength dependency of the dispersion characteristic can be suppressedby optimizing the particle diameter and refractive index of themicroparticles.

[0101] For forming the samples of the light diffusing sheets, MMA with arefractive index of 1.49 was used as a base material, and a copolymerresin of MMA and styrene (MS resin) was used for forming the lightdiffusing microparticles. Nine kinds of light diffusing microparticleshaving refractive indices in a range of 1.52 to 1.55 (refractive indexdifference Δn: 0.03 to 0.06) and average particle diameters in a rangeof 4 μm to 13.3 μm were produced by adjusting the mix proportion ofcomponents of the MS resin.

[0102] A screen 3 was configured as shown in FIG. 9, using a lightdiffusing sheet thus obtained, and the screen 3 was mounted on arear-projection display and was made to display a white display so thatluminances and color temperatures of display light at the center portionof the screen were measured at angles varied in the vertical directionswith respect to a front direction (normal direction) as a reference.

[0103] As described above, light with an extremely high directivity isincident on the screen 3. Since such light is collimated by the Fresnellens sheet 31 and then diffused only in the horizontal direction by thelenticular lens sheet 34, the light is incident on the light diffusingsheet 33 in a state of being diffused only in the horizontal directionand still maintaining the sharp directivity in the vertical direction.

[0104] In the foregoing configuration, the Fresnel lens sheet 31 and thelenticular lens sheet 34 do not contain light diffusing microparticles,and hence are transparent. Therefore, since only the light diffusingmicroparticles mixed in the light diffusing sheet 33 serve as thediffusing factor in the vertical direction, the diffusion characteristicof the light diffusing microparticles is evaluated by the foregoingmeasurement.

[0105] It should be acknowledged that when a white diffusing plate thatis considered to perform substantially complete reflection was used inplace of the rear-projection screen and reflected light was measured, auniform reflection luminance and a uniform color temperature that didnot vary with a measurement angle were detected. The color temperaturein that case was approximately 11000 K.

[0106]FIGS. 1 and 2 show the outcomes of the evaluation of the colortemperatures and the luminances of light diffusing sheets utilizingthree kinds of light diffusing microparticles with refractive indices of1.53 (Δn=0.04), 1.53 (Δn=0.04), and 1.55 (Δn=0.06), and average particlediameters of 4.0 μm (Δn×d=0.16 μm), 7.2 μm (Δn×d=0.29 μm), and 13.3 μm(Δn×d=0.80 μm), respectively, selected from among the aforementionednine kinds of light diffusing microparticles.

[0107] In FIGS. 1 and 2, the horizontal axis indicates a measurementangle (modular angle) modulated according to an angle at which theluminance declines to ⅓ of a peak value of the same (referred to as a βangle, which is regarded as representing an approximately practicalvisual field). Thus, by using the modular angle, it is possible tocompare diffusion patterns and color temperature characteristics,independently from an absolute quantity of diffusion.

[0108] In the case where light diffusing microparticles satisfyingΔn×d=0.16 were used, the color temperature when observed in the normaldirection of the screen was low, and the color temperature rose as theobservation angle (angle between the observing direction and the normalline of the screen) increased (FIG. 1). This shows that blue light rayswith a short wavelength were diffused more than red light rays with along wavelength were diffused, and hence, the red light rays weredistributed in the vicinity of the normal direction at a relatively highproportion, while the proportion of the blue light rays increased as theobservation angle increased. This substantially agrees with an outcomeof simulation on the assumption that the wavelength dependency ofdiffusion occurs according to the wavelength dependency of Δn. Besides,the diffusion pattern was found to excel in the diffusion to thevicinity of the normal direction, and had a profile of relatively lessdistribution to greater-angle directions (FIG. 2).

[0109] In the case where light diffusing microparticles satisfyingΔn×d=0.29 μm were used, like in the case of Δn×d=0.16, the wavelengthdependency of the diffusion took place according to the wavelengthdependency of Δn. These light diffusing microparticles were equivalentto those that conventionally have been used in the light diffusing sheetso as to prevent a light source behind from being seen, that is, toprevent so-called see-through.

[0110] The foregoing tendency was suppressed when Δn×d was increased,and in the case where light diffusing microparticles satisfyingΔn×d=0.80 were used, to the contrary, the color temperature lowered whenthe observation angle increased in the vicinity of the normal direction(FIG. 1). Thus, the curve shown in FIG. 1 changed from an approximate Ushape to an approximate W shape when Δn×d was increased. Furthermore,the diffusion pattern became such that the diffusion in the vicinity ofthe normal direction and its vicinity relatively decreases, therebyhaving a profile of relatively great distribution to greater-angledirections (FIG. 2).

[0111] As a result of further detailed examination, it is preferable toset Δn×d of the light diffusing microparticles in the vicinity of 0.2 μmto obtain a diffusion pattern excelling in the diffusion in the vicinityof the normal direction, and it was confirmed that the diffusion patternexhibits substantially no change when Δn×d is in a range of 0.1 μm to0.3 μm. When Δn×d exceeded the foregoing range, the diffusion patternhad a relatively steep peak in the vicinity of the normal direction andlower slopes. Besides, the wavelength dependency occurred in thediffusion pattern and the tendency of having a steep peak in the normaldirection and lower slopes becomes more remarkable as the wavelength wasshorter. This tendency is considered to affect so as to reduce thewavelength dependency of the diffusion characteristic due to thewavelength dependency of the refractive index difference Δn.

[0112] Color temperature shifts of the aforementioned nine diffusingsheet samples are plotted as change quantities from color temperaturesdetected in the normal direction to color temperatures measured at βangles, respectively, in a graph of FIG. 3. In FIG. 3, the horizontalaxis indicates a product of a difference Δd between refractive indicesof the light diffusing microparticles and the base used therein and anaverage particle diameter d, that is, Δn×d, and the vertical axisindicates a color temperature shift at the βangle (a change quantityfrom the color temperature in the normal direction). Each measured valueis plotted with a solid square “♦” and an approximate straight line isapplied. The color temperature shift (from the normal direction to the βangle (Front→β) is minimized in the vicinity of Δn×d=0.7 μm. Among thenine samples, the sample using the light diffusing microparticles thathad a refractive index of 1.55 (Δn=0.06) and an average particlediameter of 13.3 μm (Δn×d=0.80 μm) exhibited the smallest colortemperature shift, which was −410 K. This sample was one of the sampleswhose characteristics are shown in FIGS. 1 and 2.

[0113] It should be noted that since the average particle diameter, 13.3μm, of the light diffusing microparticles was relatively great, a greatamount of the light diffusing microparticles had to be dispersed so thatthe prescribed angle of visibility was obtained, and it also caused thelight diffusing sheet to have a rougher surface, thereby causing thediffusing sheet to tend to have a defect upon lamination.

[0114] Therefore, based on the thus obtained knowledge, light diffusingmicroparticles made of styrene with an average particle diameter of 6.4μm and a refractive index of 1.59 (Δn×d=0.64 μm) were produced as asample, in order to satisfy the optimal condition of Δn×d≈0.7 and torealize effective diffusion with the smallest possible mix proportion ofthe light diffusing microparticles to improve the surface condition, anda screen was produced using the sample and was evaluated. As a result, agood outcome was obtained, with a color temperature shift of 600 K.Measured values are shown with * in FIG. 3.

[0115] This confirms that the screen utilizing a newly prepared sampleof light diffusing microparticles also exhibited the characteristicsindicated by the correlation line that was obtained from the ninesamples of light diffusing microparticles, and show that the colortemperature shift can be controlled by adjusting Δn×d. It also can beseen that the diffusion characteristic substantially equivalent to thatin the case where light diffusing microparticles with a relatively greatdiameter are used can be realized with a smaller mix proportion of thelight diffusing microparticles.

[0116] It should be noted that the color temperature shift of not morethan 2000 K is a practically acceptable range. According to FIG. 3, apractically acceptable color temperature characteristic can be obtainedin the range of the practical angle of visibility β by setting Δn×d in arange of 0.5 μm to 0.9 μm. To obtain a further excellent colortemperature characteristic, Δn×d preferably is set in a range of 0.6 μmto 0.8 μm.

[0117] The above description is based on an outcome of experiments of aconfiguration in which the base and the light diffusing microparticlesare made of at least one selected from MMA, styrene, and a copolymer ofthe same, but as long as they are made of a transparent resin material,the same tendency that the wavelength dispersion of the refractive indextends to increase as the material has a greater refractive index can beseen. For instance, in the case where light diffusing microparticlesmade of a polycarbonate-based material are used, a similar outcome isobtained.

[0118] Furthermore, the foregoing description takes, as an example, acase where light diffusing microparticles were dispersed in the lightdiffusing sheet 33 of the screen 3 shown in FIG. 9 so as to simplify thepreparation of the samples and the evaluation of the same. However, inthe case where light diffusing microparticles are dispersed inside thelenticular lens sheet 32 in a screen configuration as shown in FIG. 6,this configuration is identical to the configuration described above inthe aspect that the diffusion in the vertical direction relies on thelight diffusing microparticles dispersed therein, and the configurationalso exhibits the same characteristics as those shown in FIGS. 1 to 3.

[0119] On the basis of the foregoing outcomes, the following descriptionwill depict a preferred embodiment of the aspect I of the presentinvention as to a rear-projection screen that achieves excellentcharacteristics, and a rear-projection display in which this screen isused.

[0120] Embodiment I-1

[0121] A rear-projection screen of the present embodiment, for instance,has a configuration as shown in FIG. 6, and includes at least alenticular lens sheet 32 and a Fresnel lens sheet 31. The lenticularlens sheet 32 contains, in a base thereof made of a resin material,light diffusing microparticles made of a resin material having arefractive index different from that of the base. The light diffusingmicroparticles satisfy Formula I-1 below:

0.5 μm≦ΔN 1×d 1≦0.9 μm  Formula I-1

[0122] where ΔN1 represents a difference between a refractive index ofthe light diffusing microparticles and a refractive index of the basematerial of the lenticular lens sheet, and d1 represents an averageparticle diameter of the light diffusing microparticles.

[0123] As materials for the base and the light diffusing microparticles,a combination of generally-used resin materials can be used that has acharacteristic in that the Abbe constant νd decreases (dispersionincreases) as the refractive index increases as shown in FIG. 10.

[0124] In other words, it is possible to select and use resin materialsfor the light diffusing microparticles and the lenticular lens sheet 32so as to satisfy Formula I-3 below:

(n 1−n 2)×(ν1−ν2)<0  Formula I-3

[0125] where n1 and ν1 represent a refractive index and an Abbeconstant, respectively, of the material forming the light diffusingmicroparticles and n2 and ν2 represent a refractive index and an Abbeconstant, respectively, of a material forming the lenticular lens sheet32 in which the light diffusing microparticles are dispersed.

[0126] As shown in FIG. 6, the rear-projection screen 3 includes thelenticular lens sheet 32 and the Fresnel lens sheet 31 that are disposedin parallel with each other and whose bases both are made of transparentresin materials.

[0127] The lenticular lens sheet 32 can be formed by utilizing atransparent resin such as MMA, styrene, or a copolymer resin of thesame, to form its base, and dispersing therein the light diffusingmicroparticles made of the transparent resin with a refractive indexdifferent from that of the base so that the light diffusingmicroparticles serve as an isotropic diffusing element. Here, nolimitation is on a producing method, and a method is applicable in whicha light diffusing sheet produced beforehand in a flat plate shape bycasting, injection molding, or extrusion is hot-pressed so as to have alenticular lens form, or a roll extrusion method in which a resin isshaped while extruded using a roll-shaped die in a reversed shape of adesired lenticular lens shape, or the like.

[0128] As shown in Formula I-1, by setting a product Δn×d of therefractive index difference Δn between the light diffusingmicroparticles and the base and the average particle diameter d of thelight diffusing microparticles so as to be in a range of 0.5 μm to 0.9μm, a rear-projection screen that excels in the color temperaturecharacteristic, that is, that undergoes a color variation of not morethan 2000 K in the range of the practical angle of visibility β, can berealized using materials having general wavelength dispersioncharacteristics to form the light diffusing microparticles and the base.

[0129] It should be noted that, in the foregoing configuration, sincethe diffusing effect relatively decreases in the vicinity of the normaldirection, belt-like bright regions (bright lines) extending in thehorizontal direction, called hot bands, are observed in some cases whenthe foregoing screen is used for configuring a rear-projection display.

[0130] In such a case, it is preferable to add, to the lenticular lenssheet 32, the foregoing light diffusing microparticles satisfyingFormula I-1 as a main diffusing element, and light diffusingmicroparticles that are made of a resin material having a refractiveindex different from that of the base of the lenticular lens sheet 32and that satisfy Formula I-5 below, as a sub diffusing element:

0.1 μm≦ΔNs×ds≦0.3 μm  Formula I-5

[0131] where ΔNs represents a difference between a refractive index ofthe light diffusing microparticles serving as the sub diffusing elementand a refractive index of the lenticular lens sheet base containing thesame, and ds represents an average particle diameter of the lightdiffusing microparticles serving as the sub diffusing element.

[0132] With this configuration, the diffusion in the vicinity of thenormal direction can be improved, thereby making it possible to avoid adefect such that the light source behind is seen through. The additionof the sub light diffusing microparticles diffusing element preferablyis limited to a minimum amount necessary for the avoidance of the defectthat the light source is seen through the screen. This is because thecolor temperature characteristic of the diffusion sometimes is impairedwhen the effect of the sub light diffusing microparticles on the angleof visibility exceeds the effect of the main light diffusingmicroparticles.

[0133] Generally, the diffusing function increases as a concentration Aof the dispersed light diffusing microparticles increases, as the layercontaining the light diffusing microparticles (diffusing layer) has agreater thickness t, as the light diffusing microparticles have asmaller average particle diameter d, and as the difference Δn from therefractive index of the base increases, and further, the diffusionfunction substantially is proportional to Δ×t/d×Δn.

[0134] Therefore, to prevent the aforementioned defects, it ispreferable that an average particle diameter dm and a mix proportion byvolume Am of the light diffusing microparticles as the main diffusingelement, a thickness tm of a base layer containing the light diffusingmicroparticles as the main diffusing element, a difference ΔNm between arefractive index of the light diffusing microparticles as the maindiffusing element and a refractive index of the base containing theforegoing light diffusing microparticles, an average particle diameterds and a mix proportion by volume As of the light diffusingmicroparticles as the sub diffusing element, a thickness ts of a baselayer containing the light diffusing microparticles as the sub diffusingelement, a difference ΔNs between a refractive index of the lightdiffusing microparticles as the sub diffusing element and a refractiveindex of the base containing the foregoing light diffusingmicroparticles are set so as to satisfy Formula I-6 below:

Am×tm/dm×ΔNm>As×ts/ds×ΔNs  Formula I-6

[0135] It should be noted that in the case where the lenticular lenssheet 32 is made to contain the main light diffusing microparticles andthe sub light diffusing microparticles, the lenticular lens sheet 32 maybe configured in a multi-layer form in which the main and sub lightdiffusing microparticles are dispersed in the same layer, or in amulti-layer form in which the main and sub light diffusingmicroparticles are dispersed in different layers, respectively. In theformer case, the thickness tm and the thickness ts in Formula I-6coincide with each other.

[0136] A configuration in which a lenticular lens array whose lengthwisedirection is directed in the horizontal direction is provided on alight-projected side of the Fresnel lens sheet 31 is effective also tosuppress the aforementioned hot bands.

[0137] Since the lenticular lenses effectively diffuse light in alimited angle range due to a refraction effect at an interface with air,they have an excellent characteristic in the diffusion in the vicinityof the normal direction, and provide a significant effect in suppressingthe hot bands. In the case where the diffusion angle is set excessivelygreat, however, this diffusion along with the diffusion by the lightdiffusing microparticles dispersed in the lenticular lens 32 causesmultiple diffusion, thereby impairing the resolving power. Therefore,the diffusion angle range preferably is restrained to a minimum levelrequired for reducing the hot bands. More specifically, the diffusionangle range by the lenticular lenses provided on the light-projectedside of the Fresnel lens sheet 31 preferably is approximately −3° to+3°.

[0138] Furthermore, in the case where light diffusing microparticlesalso are to be dispersed in the Fresnel lens sheet 31 with a view tosuppressing the moire effect, scintillation, etc., the light diffusingmicroparticles dispersed in the Fresnel lens sheet 31 preferably aremade of a resin material having a refractive index different from arefractive index of a base material forming the base of the Fresnel lenssheet 31, and satisfy Formula I-4 below:

0.1 μm≦ΔNf×df≦0.3 μm  Formula I-4

[0139] where ΔNf represents a difference between a refractive index ofthe light diffusing microparticles contained in the Fresnel lens sheetand a refractive index of a base of the Fresnel lens sheet, and dfrepresents an average particle diameter of the light diffusingmicroparticles contained in the Fresnel lens sheet.

[0140] In the foregoing case, the light diffusing microparticlespreferably are added to the Fresnel lens sheet 31 so that the diffusionof light by the light diffusing microparticles contained in the Fresnellens sheet 31 is smaller than the diffusion of light by the lightdiffusing microparticles contained in the lenticular lens sheet 32.

[0141] While light diffusing microparticles are added to the Fresnellens sheet 31, the light diffusing microparticles as the sub diffusingelement may be added to the lenticular lens sheet 32. A total quantityof the light diffusing microparticles preferably is in a range such thatthe effect on the angle of visibility caused by the light diffusingmicroparticles is smaller than the effect caused by the light diffusingmicroparticles that satisfy Formula I-1 and that serve as the maindiffusing element.

[0142] Embodiment I-2

[0143] A rear-projection screen of the present embodiment, for instance,has a configuration as shown in FIG. 8 or 9, and includes at least alight diffusing sheet 33, a lenticular lens sheet 32 (or 34) and aFresnel lens sheet 31. The light diffusing sheet 33 contains, in a basethereof made of a resin material, light diffusing microparticles made ofa resin material having a refractive index different from that of thebase. The light diffusing microparticles satisfy Formula I-2 below:

0.5 μm≦ΔNp×dp≦0.9 μm  Formula I-2

[0144] where ΔNp represents a difference between a refractive index ofthe light diffusing microparticles and a refractive index of the base ofthe light diffusing sheet, and dp represents an average particlediameter of the light diffusing microparticles.

[0145] As materials for the base and the light diffusing microparticles,a combination of generally-used resin materials can be used that has acharacteristic in that the Abbe constant νd decreases (dispersionincreases) as the refractive index increases as shown in FIG. 10.

[0146] In other words, it is possible to select and use resin materialsfor the light diffusing microparticles and the light diffusing sheet 33so as to satisfy Formula I-3 below:

(n 1−n 2)×(ν1−ν2)<0  Formula I-3

[0147] where n1 and ν1 represent a refractive index and an Abbeconstant, respectively, of the material forming the light diffusingmicroparticles and n2 and ν2 represent a refractive index and an Abbeconstant, respectively, of a material forming the light diffusing sheet33 in which the light diffusing microparticles are dispersed.

[0148] As shown in FIG. 8 or 9, the rear-projection screen includes thelight diffusing sheet 33, the lenticular lens sheet 32 (or 34), and theFresnel lens sheet 31 that are disposed in parallel with each other andwhose bases both are made of transparent resin materials.

[0149] The light diffusing sheet 33 can be formed by utilizing atransparent resin such as MMA, styrene, or a copolymer resin of thesame, to form its base, and dispersing therein the light diffusingmicroparticles made of the transparent resin with a refractive indexdifferent from that of the base so that the light diffusingmicroparticles serve as an isotropic diffusing element. Here, there isno limitation on a producing method, and a method is applicable in whicha light diffusing sheet produced beforehand in a flat plate shape bycasting, injection molding, or extrusion is hot-pressed so as to have alenticular lens form, or a roll extrusion method in which a resin isshaped while extruded using a roll-shaped die in a reversed shape of adesired lenticular lens shape, or the like.

[0150] In the present embodiment also, as shown in Formula I-2, bysetting a product Δn×d of the refractive index difference Δn between thelight diffusing microparticles and the base and the average particlediameter d of the light diffusing microparticles so as to be in a rangeof 0.5 μm to 0.9 μm, a rear-projection screen that excels in the colortemperature characteristic, that is, that undergoes a color variation ofnot more than 2000 K in the range of the practical angle of visibilityβ, can be realized using materials having general wavelength dispersioncharacteristics to form the light diffusing microparticles and the base.

[0151] It should be noted that, in the foregoing configuration, sincethe diffusing effect relatively decreases in the vicinity of the normaldirection, belt-like bright regions (bright lines) extending in thehorizontal direction, called hot bands, are observed in some cases whenthe foregoing screen is used for configuring a rear-projection display.

[0152] In such a case, like in Embodiment I-1, it is preferable to add,to the light diffusing sheet 33, the foregoing light diffusingmicroparticles satisfying Formula I-2 as a main diffusing element, andlight diffusing microparticles that are made of a resin material havinga refractive index different from that of the base of the lightdiffusing sheet 33 and that satisfy Formula I-5 below, as a subdiffusing element:

0.1 μm≦ΔNs×ds≦0.3 μm  Formula I-5

[0153] where ΔNs represents a difference between a refractive index ofthe light diffusing microparticles serving as the sub diffusing elementand a refractive index of the lenticular lens sheet base containing thesame, and ds represents an average particle diameter of the lightdiffusing microparticles serving as the sub diffusing element.

[0154] With this configuration, the diffusion in the vicinity of thenormal direction can be improved, thereby making it possible to avoid adefect such that the light source behind is seen through. The additionof the sub light diffusing microparticles diffusing element preferablyis limited to a minimum amount necessary for the avoidance of the defectthat the light source is seen through the screen. This is because thecolor temperature characteristic of the diffusion sometimes is impairedwhen the effect of the sub light diffusing microparticles on the angleof visibility exceeds the effect of the main light diffusingmicroparticles.

[0155] Furthermore, for the same reason as that in Embodiment I-1, it ispreferable that an average particle diameter dm and a mix proportion byvolume Am of the light diffusing microparticles as the main diffusingelement, a thickness tm of a base layer containing the light diffusingmicroparticles as the main diffusing element, a difference ΔNm between arefractive index of the light diffusing microparticles as the maindiffusing element and a refractive index of the base containing theforegoing light diffusing microparticles, an average particle diameterds and a mix proportion by volume As of the light diffusingmicroparticles as the sub diffusing element, a thickness ts of a baselayer containing the light diffusing microparticles as the sub diffusingelement, a difference ΔNs between a refractive index of the lightdiffusing microparticles as the sub diffusing element and a refractiveindex of the base containing the foregoing light diffusingmicroparticles are set so as to satisfy Formula I-6 below:

Am×tm/dm×ΔNm>As×ts/ds×ΔNs  Formula I-6

[0156] It should be noted that in the case where the light diffusingsheet 33 is made to contain the main light diffusing microparticles andthe sub light diffusing microparticles, the light diffusing sheet 33 maybe configured in a multi-layer form in which the main and sub lightdiffusing microparticles are dispersed in the same layer, or in amulti-layer form in which the main and sub light diffusingmicroparticles are dispersed in different layers, respectively. In theformer case, the thickness tm and the thickness ts in Formula I-6coincide with each other.

[0157] Furthermore, like in Embodiment I-1, a configuration in which alenticular lens array whose lengthwise direction is directed in thehorizontal direction is provided on a light-projected side of theFresnel lens sheet 31 is effective also, to suppress the aforementionedhot bands. Here, like in Embodiment I-1, the diffusion angle range bythe lenticular lenses provided on the light-projected side of theFresnel lens sheet 31 preferably is approximately −3° to +3°.

[0158] Furthermore, in the case where light diffusing microparticlesalso are to be dispersed in the Fresnel lens sheet 31 with a view tosuppressing the moiré effect, scintillation, etc., the light diffusingmicroparticles dispersed in the Fresnel lens sheet 31 preferably aremade of a resin material having a refractive index different from arefractive index of a base material forming the base of the Fresnel lenssheet 31, and satisfy Formula I-4 below:

0.1 μm≦ΔNf×df≦0.3 μm  Formula I-4

[0159] where ΔNf represents a difference between a refractive index ofthe light diffusing microparticles contained in the Fresnel lens sheetand a refractive index of a base of the Fresnel lens sheet, and dfrepresents an average particle diameter of the light diffusingmicroparticles contained in the Fresnel lens sheet.

[0160] In the foregoing case, the light diffusing microparticlespreferably are added to the Fresnel lens sheet 31 so that the diffusionof light by the light diffusing microparticles contained in the Fresnellens sheet 31 is smaller than the diffusion of light by the lightdiffusing microparticles contained in the light diffusing sheet 33.

[0161] While light diffusing microparticles are added to the Fresnellens sheet 31, the light diffusing microparticles as the sub diffusingelement may be added to the light diffusing sheet 33. A total quantityof the light diffusing microparticles preferably is in a range such thatthe effect on the angle of visibility caused by the light diffusingmicroparticles is smaller than the effect caused by the light diffusingmicroparticles that satisfy Formula I-2 and that serve as the maindiffusing element.

[0162] Embodiment I-3

[0163] A rear-projection screen of the present embodiment, for instance,has a configuration as shown in FIG. 6, and includes at least alenticular lens sheet 32 and a Fresnel lens sheet 31. The lenticularlens sheet 32 and the Fresnel lens sheet 31 contain, in bases thereofmade of resin materials, light diffusing microparticles made of resinmaterials having refractive indices different from those of the basesthereof, respectively. The light diffusion caused by the light diffusingmicroparticles contained in the Fresnel lens sheet 31 is smaller thanthe light diffusion caused by the light diffusing microparticlescontained in the lenticular lens sheet 32, and the light diffusingmicroparticles contained in the Fresnel lens sheet 31 satisfy FormulaI-4 below:

0.1 μm≦ΔNf×df≦0.3 μm  Formula I-4

[0164] where ΔNf represents a difference between a refractive index ofthe light diffusing microparticles contained in the Fresnel lens sheetand a refractive index of the base of the Fresnel lens sheet, and dfrepresents an average particle diameter of the light diffusingmicroparticles contained in the Fresnel lens sheet.

[0165] Alternatively, a rear-projection screen of the presentembodiment, for instance, has a configuration as shown in FIG. 8 or 9.In this case, the rear-projection screen includes at least a lightdiffusing sheet 33, a lenticular lens sheet 32 (or 34) and a Fresnellens sheet 31. The light diffusing sheet 33 and the Fresnel lens sheet31 contain, in bases thereof made of resin materials, light diffusingmicroparticles made of resin materials having refractive indicesdifferent from those of the bases, respectively. The light diffusioncaused by the light diffusing microparticles contained in the Fresnellens sheet 31 is smaller than the light diffusion caused by the lightdiffusing microparticles contained in the light diffusing sheet 33, andthe light diffusing microparticles contained in the Fresnel lens sheet31 satisfy Formula I-4 below:

0.1 μm≦ΔNf×df≦0.3 μm  Formula I-4

[0166] where ΔNf represents a difference between a refractive index ofthe light diffusing microparticles contained in the Fresnel lens sheetand a refractive index of the base of the Fresnel lens sheet, and dfrepresents an average particle diameter of the light diffusingmicroparticles contained in the Fresnel lens sheet.

[0167] In the present embodiment, by setting ΔNf×df in a range of 0.1 μmto 0.3 μm, a diffusion characteristic excelling in the diffusing effectin the vicinity of the normal direction and effective for suppressingthe scintillation can be obtained. Furthermore, since diffusioncomponents in directions at relatively greater angles are small, theimpairment of the resolving power is minimized, and the proportion ofoptical loss is small even in combination with the BS-providedlenticular lens sheet.

[0168] The Fresnel lens sheet 31 can be formed by utilizing atransparent resin such as MMA, styrene, or a copolymer resin of thesame, to form its base, and dispersing therein the light diffusingmicroparticles made of the transparent resin with a refractive indexdifferent from that of the base so that the light diffusingmicroparticles serve as an isotropic diffusing element. Here, there isno limitation on a producing method, and a method is applicable in whicha light diffusing sheet produced beforehand in a flat plate shape bycasting, injection molding, or extrusion is hot-pressed so as to have aFresnel lens form, or a method in which the light diffusing sheet isused as a base on which an ultraviolet-hardening resin is applied so asto have the Fresnel lens shape, or the like.

[0169] The Fresnel lens sheet provides an effect of suppressing the hotbands that tend to be remarkable as the color temperature characteristicis improved, particularly when the Fresnel lens sheet is used incombination with the lenticular lens sheet or the light diffusing sheetwith an improved color temperature characteristic as in Embodiment I-1or Embodiment I-2.

[0170] Embodiment I-4

[0171] A rear-projection display of the present embodiment has aconfiguration shown in FIG. 4, and includes a rear-projection screendescribed above. It should be noted that FIG. 4 is a perspective view toshow how principal elements are arranged.

[0172] In this display, three principal-color images formed on CRTs 1(1R, 1G, and 1B) are enlarged and projected by projection lenses 2 (2R,2G, and 2B), respectively. The three principal-color images reflected bya mirror 71 are superimposed on a screen 3, thereby forming a colorimage, and are diffused due to the effect of the screen 3 so as to beobservable as an image at various angles. These members are arrangedinside a cabinet 72 that prevents external light from entering thedevice.

[0173] The screen 3 is configured as shown in FIG. 6 or 8. In the casewhere the screen 3 has a configuration shown in FIG. 6, light diffusingmicroparticles whose Δn×d is set so as to be in a range of 0.5 μm to 0.9μm as described above are contained in a light diffusing sheet 32. Inthe case where the screen 3 has a configuration shown in FIG. 8, lightdiffusing microparticles whose Δn×d is set so as to be in a range of 0.5μm to 0.9 μm as described above are contained in a light diffusing sheet33. This configuration allows the wavelength dependency of the diffusioncaused by the light diffusing microparticles to be suppressed to aminimum level, and a rear-projection display excelling in the colortemperature characteristic, that is, that undergoes a color variation ofnot more than 2000 K in the range of the practical angle of visibilityβ, can be realized.

[0174] Embodiment I-5

[0175] A rear-projection display of the present embodiment has aconfiguration shown in FIG. 5, and includes a rear-projection screendescribed above. It should be noted that FIG. 5 also is a perspectiveview so as to show how principal elements are arranged.

[0176] In this display, a projection optics unit 9 is provided. In theprojection optics unit 9, a lamp as a light source, an illuminatingoptical system, a color separation optical system, a liquid crystalpanel, a color synthesizing optical system, and the like are providedappropriately, and images are formed by spatial modulation of projectedlight by a liquid crystal panel. These images are enlarged and projectedby a projection lens 6. The projected light reflected by a mirror 71 isbrought into focus on a screen 3, and is diffused due to the effect ofthe screen 3, so as to be observable as an image at various angles.These members are arranged inside a cabinet 72 that prevents externallight from entering the device.

[0177] The screen 3 is configured as shown in FIG. 6, 8, or 9; however,to make the best use of the characteristic in that the color shiftcorrection is unnecessary, the screen 3 preferably has a configurationshown in FIG. 9. A Fresnel lens sheet 31, as described above, containslight diffusing microparticles whose Δn×d is set so as to be in a rangeof 0.1 μm to 0.3 μm. This allows a diffusion characteristic excelling inthe diffusing effect in the vicinity of the normal direction andeffective for suppressing scintillation to be obtained. Furthermore,since diffusion components in directions at relatively greater anglesare small, the impairment of the resolving power is minimized, and theproportion of optical loss is small even in combination with theBS-provided lenticular lens sheet 34.

[0178] Furthermore, by dispersing light diffusing microparticles whoseΔn×d is set so as to be in a range of 0.5 μm to 0.9 μm in the lightdiffusing sheet 33 in the case where the screen 3 has a configurationshown in FIG. 9 or 8, or by dispersing the light diffusingmicroparticles in the lenticular lens sheet 32 in the case where thescreen has a configuration shown in FIG. 6, a rear-projection displaywith a minimum of color variation with respect to an observation angleis obtained.

[0179] Aspect II of the Present Invention

[0180] The inventors discovered that significant scintillation wascaused because a diffusing layer of a laminated lenticular lens sheetused in a conventional rear-projection display was disposedsubstantially in the vicinity of a focal plane of a lenticular lensarray.

[0181]FIG. 17 is a partially enlarged view of a laminated lenticularlens sheet used in a conventional rear-projection display, and shows raytrajectories as well.

[0182] As shown in FIG. 7, a conventional laminated lenticular lenssheet 36 is formed by laminating a lenticular lens film 362 and a lightdiffusing sheet 361 with a transparent adhesive layer 363. The adhesivelayer 363 usually has a thickness of approximately 20 μm to 50 μm.

[0183] As is seen in FIG. 17, projected light is converged on a focalplane, in the vicinity of a focus of each lenticular lens 3621. Sinceblack stripes 3622 are provided on light non-transmission regions in thevicinity of the focal plane, the black stripes 3622 effectively absorbexternal light without blocking the projected light, thereby preventingthe contrast from deteriorating due to external light.

[0184] The diffusing layer 3612 is provided extremely close to the focalplane, separated from the focal plane by the thickness of thetransparent adhesive layer 363. Consequently, the projected light isbrought into focus in limited regions in the diffusing layer 3612, andlight diffusing microparticles in the focus regions are irradiated withlight with an extremely high intensity, while light diffusingmicroparticles in the other regions do not contribute to the diffusion.

[0185] The inventors have discovered that the light diffusingmicroparticles thus irradiated with intense light at limited regionscause significant scintillation. The following description will depictan embodiment of the aspect II of the present invention.

[0186] Embodiment II-1

[0187]FIG. 11 shows a cross section in the horizontal direction of arear-projection display according to an embodiment of the aspect II ofthe present invention. In FIG. 11, members having the same structuresand functions as those shown in FIG. 16 illustrating a conventionalrear-projection display will be designated by the same referencenumerals, and descriptions of the same will be omitted. It should benoted that, though not shown, the display may include a mirrorreflecting projected light enlarged and projected by the projection lens6, and a cabinet housing an optical system and preventing external lightfrom entering, as shown in FIG. 5.

[0188] Characteristics of the aspect II of the present invention shownin FIG. 11 are that a transparent Fresnel lens sheet 81 is used, ascompared with the conventional rear-projection display provided with aFresnel lens sheet in which a diffusing material is dispersed forsuppressing scintillation, and that a transparent layer 823 is providedbetween a focal plane of a lenticular lens array of a laminatedlenticular lens sheet 82 and a diffusing layer 8212.

[0189]FIG. 12 is a horizontal-direction partially-enlarged viewillustrating the lenticular lens sheet 82 part of a rear-projectiondisplay according to the aspect II of the present invention, and showsray trajectories as well.

[0190] As shown in FIG. 12, the lenticular lens film 822 includeslenticular lenses 8221 that are provided on the light-incident side andwhose lengthwise direction is directed in the vertical direction. Thelenticular lens film 822 has a thickness set so that the focus positionof each lenticular lens 8221 substantially coincides with thelight-exiting surface of the film. Therefore, light non-transmissionregions that the projected light does not pass through and whoselengthwise direction is directed in the vertical direction are providedin a stripe form. On the light non-transmission regions, light absorbinglayers (black stripes) 8222 are provided in a stripe form.

[0191]821 denotes a diffusing sheet, which is obtained by laminating adiffusing layer 8212 and a transparent layer 8211. The light absorbinglayers 8222-side surface of the lenticular lens film 822 and thediffusing layer 8212-provided surface of the diffusing sheet 821 aremade to adhere to each other with the transparent layer 823 interposedtherebetween.

[0192] In FIG. 12, f1 represents a distance from valleys of thelenticular lens array to the focal plane of the lenticular lens array,t1 represents a distance from the focal plane of the lenticular lensarray to a light-projected side (spatial modulation element-side)surface of the diffusing layer 8212, and t2 represents a distance fromthe focal plane of the lenticular lens array to an image-observed-sidesurface of the diffusing layer 8212. The aspect II of the presentinvention is intended to allow the generation of scintillation to beminimized by setting t1 appropriately, and to allow a high resolvingpower to be maintained by setting t2 appropriately.

[0193] The following description will depict requirements forsuppressing scintillation.

[0194] The thickness of the transparent layer 823 is not less than thedistance f1 between the valleys of the lenticular lens array and thefocal plane of the lenticular lens array, and therefore causes thedistance t1 between the light-projected-side surface of the diffusinglayer 8212 and the focal plane of the lenticular lens array to be notless than f1.

t 1≦f 1

[0195] In a configuration as shown in FIG. 12, light converged in thevicinity of the focal plane by the function of the lenticular lens arrayis incident on the diffusing layer 8212, having a width not less than apitch P1 of the lenticular lenses 8221. Consequently, an averageluminance in an effective region that is formed by light incident on onelenticular lens unit and reaching the diffusing layer 8212 can be madenot more than a luminance of the projected light upon incidence on thelenticular lens. It should be noted that in the vicinity of eachlight-incident region through which light from each lenticular lens 8221is incident on the diffusing layer 8212, projected light from adjacentlenticular lenses is also incident, but such light has a greatlydifferent incident angle and interferes with each other, therebygenerating no scintillation.

[0196] Thus, the foregoing configuration prevents local irradiation oflight diffusing microparticles with light of high intensity, therebysignificantly suppressing scintillation. Consequently, it is possible toobtain a sufficient display quality even in the case where a transparentFresnel lens sheet 81 is utilized in which no diffusing material isdispersed.

[0197] Scintillation is reduced as the distance between the diffusinglayer 8212 and the focal plane of the lenticular lens array increases.According to the research by the inventors of the present invention, toachieve a remarkable effect as compared with the case where thediffusing layer 8212 is provided on the focal plane, the distancebetween the diffusing layer 8212 and the lenticular lens array focalplane is required to be not less than f1 described above, and preferablyis about three times f1 described above.

[0198] The setting as described above enables significant reduction ofscintillation, but the resolving power decreases if the distance betweenthe diffusing layer 8212 and the lenticular lens array focal plane isset to be excessively great.

[0199] The following description will depict conditions for maintaininga resolving power as a second part of the aspect II of the presentinvention.

[0200] The following description will depicts a mechanism of thedecrease in the resolving power in the case where the distance betweenthe diffusing layer 8212 and the lenticular lens array focal plane isincreased, while referring to FIG. 13. To develop a clear discussion, amodel in which diffusion regions are concentrated at theimage-observed-side surface (positions at the distance t2 from the focalplane of the lenticular lens array) is discussed. Since the resolvingpower seems to decrease as the diffusing layer 8212 is provided at aposition farther from the focal plane of the lenticular lens array, aresolving power greater than that in the present model seems to beachieved in the case of the aspect II of the present invention, in whichthe diffusing layer 8212 is provided on a position further on thelight-projected side than the position described above.

[0201] Light incident on lenticular lens units provided at an arraypitch P1 in the lenticular lens array passes through a focus of eachlenticular lens unit, reaches the diffusing layer 8212 alongtrajectories as shown in FIG. 13, and is diffused according to diffusioncharacteristics of the diffusing layer 8212, which are shown withellipses in the figure. When viewed in the normal direction, the lightis observed as a beam flaring with an intensity distribution accordingto normal direction components of the foregoing ellipses as shown on theright side of FIG. 13.

[0202] As is clear from FIG. 13, the beam has a width Db expressed as:

Db=t 2×p 1/f 1

[0203] As to a rear-projection display of the aspect II of the presentinvention, even on the assumption that the diffusing effect concentrateson an image-observed-side surface of the diffusing layer 8212, thedistance t2 between the image-observed-side surface of the diffusinglayer 8212 and the lenticular lens array focal plane is set as shownbelow so that the beam width Db should be not more than a pixel pitchPg:

Db=t 2×P 1/f 1≦Pg

t 2≦Pg/P 1×f 1

[0204] By thus setting the same, it is possible to realize arear-projection display that has an excellent resolving power,undergoing a minimum of the resolving power decrease due to the screeneven with respect to a maximum spatial frequency 1/(2×Pg) that thedevice is capable of presenting.

[0205] It should be noted that transparency of the Fresnel lens sheet 81and the transparent layer 823 in the foregoing description signifiesthat a light diffusing material intended for diffusing lightsubstantially is not contained, and it does not mean completely nodiffusing effect. For instance, what normally is called as a transparentplate still has slight diffusivity due to structural unevenness, forinstance, presence of a minute amount of impurities, etc. To quantify arelatively small diffusivity, an index called haze value is often used.A haze value of not more than 1% indicates high-level transparency,while a haze value of not more than 10% is regarded as a level ofsubstantially no diffusion effect, thereby being expressed astransparent. The foregoing definition as to the “transparency” appliesto all the aspects I and II of the present invention.

[0206] Furthermore, the transparent layer 8211 provided on theimage-observed side of the diffusing layer 8212 is provided so as toincrease the mechanical strength, and makes no optical contribution.Therefore, as long as the laminated lenticular lens sheet 82 can bemaintained, it may be omitted.

[0207] Embodiment II-2

[0208] In the case where the vertical angle of visibility is limited bydecreasing the angle of diffusion by the diffusing layer 8212 so as togive precedence to a normal-direction luminance, requirements forpreventing the resolving power from decreasing can be defined withanother index shown in Embodiment II-1 above.

[0209] In this case as well, the rear-projection display has the sameconfiguration as shown in FIG. 11, and like in Embodiment II-1, tosuppress scintillation, the distance t1 between the light-projected-sidesurface of the diffusing layer 8212 and the focal plane of thelenticular lens array is set as described below:

t 1≧f 1

[0210] Assuming that a diffusion characteristic of the diffusing layer8212 can be given as below, as to an observation luminance I in the casewhere parallel light rays are incident perpendicularly, the observationluminance I can be given as a function of an observation angle θ:

I=I 0×f(θ)

I/I 0=f(θ)

[0211] where I0 represents a luminance in the normal direction of thediffusing layer, and necessarily f(0)=1.

[0212]FIG. 14 is a view schematically illustrating a state in which apulse-like incident light is observed as a beam spot with a finite rangein the case where the diffusing layer 8212 with such a diffusioncharacteristic is present at the distance t2 from the lenticular lensarray focal plane.

[0213] In FIG. 14, in order to discuss only the resolution powerdecrease due to the multiple diffusion, a pulse-like input is assumed,and further, the pitch of the lenticular lenses is assumed to beinfinite, and light is assumed to be emitted as completely diffusedlight from one point on the focal plane of the same in the horizontaldirection. Moreover, the thickness of the diffusing layer 8212 isassumed to be infinite, and the image-observed side of the diffusinglayer 8212 is assumed to be an interface with air. It should be notedthat the mechanism of expansion of the range of a beam spot in the casewhere the transparent layer 8211 is provided on the image-observed sideof the diffusing layer 8212 is identical to the mechanism describedabove.

[0214] Light emitted in the optical axis direction (φ=0) from a pointthat is on an optical axis and on the focal plane of the lenticular lensarray is incident on the diffusing layer along the optical axis, wherethe light is diffused and is allowed to leave, with a relative intensityof 1 in the optical axis direction.

[0215] On the other hand, light emitted at an angle φ from a point onthe focal plane of the lenticular lens array is incident on thediffusing layer at a position P (φ) that is at a distance of tan(φ)×t2from the optical axis on the diffusing layer, and thereafter, it isdiffused with a direction satisfying θ−a sin(n×sin(φ)) as a mainorientation direction. An optical-axis-direction component of thediffused light is f(θ) according to a diffusion intensity distributionof the diffusing layer 8212.

[0216] When observed from the optical axis direction, a light intensityof the portion viewed from the position P(φ) is f(θ), and consequently,it is observed as a spot with a profile as shown in the right side ofFIG. 14.

[0217] Now, let θ satisfying f(θ)={fraction (1/10)} be γ:

f(γ)={fraction (1/10)}

[0218] Then, a medium angle γi corresponding to the observation angle γis derived from an equation below:

γi=a sin(sin(γ)/n)

[0219]FIGS. 15A and 15B show profiles of an image observed upon assumedinputs in a pulse form with intervals Pγ satisfying Pγ=2×tan(γi)×t2.

[0220] Image signals in the pulse form results in beam spots withprofiles shown with broken lines, respectively, due to theaforementioned mechanism (FIG. 15A).

[0221] Since the pitch interval Pγ is set as described above, the beamspots cross each other at a middle point between the image signals wherea relative intensity of 0.1 is obtained.

[0222] The observer in the optical axis direction observes an image asshown in FIG. 15B, with these beam spots overlapping each other. Sincean intensity at a position at a distance of Pγ from an image position ofeach beam spot can be regarded as substantially zero, a peak value ofthe image pattern is approximately 1, and a bottom value thereof isapproximately 0.2 of the peak value.

[0223] A degree of modulation M of an image pattern is derived generallyas:

M=(Peak Value−Bottom Value)/(Peak Value+Bottom Value)

[0224] Therefore, a degree of modulation of the image pattern shown inFIG. 15B is 0.8/1.2≈0.67.

[0225] Therefore, the degree of modulation is not less than 0.67 whenthe pitch of the input image signal is not less than the foregoing Pγ,while the degree of modulation is less than 0.67 when the pitch of theinput image signal is less than the foregoing Pγ.

[0226] Generally, a resolution limit is a degree of modulation of 10%,but a degree of modulation of not less than about 70% is required so asto suppress a decrease in the resolving power to an undetectable level.

[0227] In the foregoing description, a pulse-form input is assumed so asto simplify the model for clarification of the discussion, but an actualmodulation signal of a display element is in a rectangular form. Asignal pitch of the maximum spatial frequency signal that arear-projection display having a pixel structure with a pitch Pg iscapable of presenting is 2×Pg, but taking a width of the foregoingrectangle into consideration, the pixel pitch Pg is equivalent to asignal interval in the case where the foregoing pulse-form input isassumed. Therefore, the requirements:

Pγ≦Pg

2×tan(γi)×t 2≦Pg

t 2≦Pg/2/tan(γi)

[0228] cause a degree of modulation corresponding to an input signal ofthe maximum spatial frequency 1/(2×Pg) that the display is capable ofpresenting to be not less than 0.67.

[0229] Since the rear-projection display according to the aspect II ofthe present invention is configured so that the distance t2 from thefocal plane of the lenticular lens array to the image-observed-sidesurface of the diffusing layer 8212 satisfies the foregoing expressionsof relationships, the rear-projection display excels in resolution,having a degree of modulation of 0.67 even with respect to the maximumspatial frequency of 1/(2×Pg) that the device is capable of presenting.

[0230] Furthermore, since the distance t1 between thelight-projected-side surface of the diffusing layer 8212 and the focalplane of the lenticular lens array is set so as to be not less than f1,scintillation can be reduced significantly as compared with the casewhere the diffusion layer is provided in the vicinity of the focalplane. Though conventionally a diffusing material is mixed in theFresnel lens sheet so as to reduce scintillation, this configurationeither makes the addition of the diffusing material unnecessary orallows the quantity of the diffusing material mixed therein to decreasesignificantly. Therefore, the drawback in that the efficiency lowers dueto the diffusing material mixed in the Fresnel lens sheet and thedrawback in that the resolving power rapidly decreases in the case wherean air gap is produced can be avoided or reduced significantly.

[0231] Embodiment II-3

[0232] The foregoing description is made from the viewpoint of makingthe best use of the display capability of the display element used inthe device, and the following description will depict an embodiment of arear-projection screen according to the aspect II of the presentinvention that achieves a resolving power necessary from the viewpointof the human visual performance.

[0233] The configuration of the screen per se is the same as that shownin FIG. 11, and to suppress scintillation, like in the embodiments II-1and II-2, the distance t1 between the light-projected-side surface ofthe diffusing layer 8212 and the focal plane of the lenticular lensarray is set as described below.

t 1≧f 1

[0234] The human visual acuity is expressed by a reciprocal of a valuethat is obtained by converting a resolvable interval into an angle inunits of minutes. For instance, the visual acuity is 1 when theresolving power of eyes corresponds to 1 minute as an angle, the visualacuity is 2 when the resolving power of eyes corresponds to 0.5 minuteas an angle, and the visual acuity is 0.5 when the resolving power ofeyes corresponds to 2 minutes as an angle.

[0235] On the other hand, a rear-projection projector is suitable for alarge-size screen, and mainly applied to a large screen with a diagonalof not less than 50 inches. Generally, a visual range suitable for imageobservation is three times a height of a screen. Since a50-inch-diagonal screen with an aspect ratio of 4:3 has a height ofapproximately 0.75 m, a suitable visual range is approximately 2.3 m.

[0236] A width Ps that corresponds to an average human visual acuity of1 and a distance of 2.3 m is:

Ps=2.3 m×tan(1 minute)≈0.7 mm

[0237] As long as a rear-projection screen is capable of resolving aninterval of 0.7 mm sufficiently, the rear-projection screen isconsidered to have a sufficient resolving power irrespective of thenumber of pixels of a display element used in a rear-projection display.

[0238] As to a rear-projection screen according to the aspect II of thepresent invention, a distance t2 between an image-observed-side surfaceof the diffusing layer 8212 to the focal plane of the lenticular lensarray is set as shown below, so that a range Db of a beam spotcorresponding to input signals in a pulse form is not more than Ps=0.7mm:

Db=t 2×P 1/f 1≦0.7 mm

t 2≦0.7 mm/P 1×f 1

[0239] With the setting as above, a rear-projection screen is capable ofresolving an interval of 0.7 mm sufficiently. Therefore it has asufficient resolving power irrespective of the number of pixels of adisplay element used in rear-projection display.

[0240] Furthermore, since the distance t1 between thelight-projected-side surface of the diffusing layer 8212 and the focalplane of the lenticular lens array is set to be not less than f1,scintillation can be reduced significantly as compared with the casewhere the diffusing layer is provided in the vicinity of the focalplane. Though conventionally a diffusing material is mixed in theFresnel lens sheet so as to reduce scintillation, this configurationeither makes the addition of the diffusing material unnecessary orallows the quantity of the diffusing material mixed therein to decreasesignificantly. Therefore, the drawback in that the efficiency lowers dueto the diffusing material mixed in the Fresnel lens sheet and thedrawback in that the resolving power rapidly decreases in the case wherean air gap is produced can be avoided or reduced significantly.

[0241] Embodiment II-4

[0242] Furthermore, in the case where a vertical visual angle is limitedby decreasing an angle of diffusion by the diffusing layer 8212 so as togive precedence to a normal-direction luminance, requirements forpreventing the resolving power from decreasing can be defined with thesame indices as those of the theory in Embodiment II-2 above.

[0243] In this case as well, the rear-projection display has the sameconfiguration as shown in FIG. 11, and like in Embodiment II-1, tosuppress scintillation, the distance t1 between the light-projected-sidesurface of the diffusing layer 8212 and the focal plane of thelenticular lens array is set as described below:

t 1≧f 1

[0244] As shown in Embodiment II-3, a resolution interval required of arear-projection screen is 0.7 mm.

[0245] As to a rear-projection screen according to the aspect II of thepresent invention, a distance t2 between an image-observed-side surfaceof the diffusing layer 8212 to the focal plane of the lenticular lensarray is set as shown below, by substituting 0.7 mm for the signalinterval 2×Pg corresponding to the maximum spatial frequency that therear-projection display depicted in the description of Embodiment II-2is capable of presenting:

2×tan(γi)×t 2≦0.7 mm

t 2≦0.35 mm/tan(γi)

[0246] With the setting as above, a rear-projection screen is capable ofresolving an interval of 0.7 mm sufficiently. Therefore it has asufficient resolving power irrespective of the number of pixels of adisplay element used in rear-projection display.

[0247] Furthermore, since the distance t1 between thelight-projected-side surface of the diffusing layer 8212 and the focalplane of the lenticular lens array is set to be not less than f1,scintillation can be reduced significantly as compared with the casewhere the diffusing layer is provided in the vicinity of the focalplane. Though conventionally a diffusing material is mixed in theFresnel lens sheet so as to reduce scintillation, this configurationeither makes the addition of the diffusing material unnecessary orallows the quantity of the diffusing material mixed therein to decreasesignificantly. Therefore, the drawback in that the efficiency lowers dueto the diffusing material mixed in the Fresnel lens sheet and thedrawback in that the resolving power rapidly decreases in the case wherean air gap is produced can be avoided or reduced significantly.

EXAMPLES

[0248] The following description will depict examples of the aspect IIof the present invention, along with comparative examples.

[0249] In each of the examples and comparative examples, a displayelement with 720 pixels in the vertical direction×1280 pixels in thehorizontal direction was used as a projection system, and an image wasprojected by 7% over-scan to a 52-inch-diagonal screen with an aspectratio of 16:9 (648 mm in the vertical direction×1151 mm in thehorizontal direction).

[0250] Therefore, a pixel pitch Pg on the screen was 0.96 mm.

[0251] Furthermore, a lenticular lens film was made of an acrylic resinwith a refractive index n=1.5, and a lenticular lens pitch P1 and amaximum light-exiting angle due to lens refraction were set to be 0.15mm and 45° (in-medium equivalent angle of 28°), respectively. With theforegoing setting, the distance f1 between the valleys and the focalplane of the lenticular lens array was approximately 0.14 mm.

[0252] The lenticular lens film 822 had a thickness set so that thelight-exiting surface coincided with the focal plane, and lightabsorbing layers (black stripes) 8222 with a width of 100 μm (⅔ of alenticular lens pitch) each were provided on the light non-transmissionportions of the light-exiting surface.

[0253] In the examples and comparative examples described below, thelenticular lens films 822 were used so that laminated lenticular lenssheets 82 that differed in conditions of the diffusing layers 8212 wereproduced.

Example 1

[0254] A pellet made of an acrylic resin with a refractive index ofapproximately 1.5 as a base in which were dispersed light diffusingmicroparticles with an average particle diameter of approximately 6 μmmade of a MS resin (copolymer of MMA and styrene) with a refractiveindex of 1.55, and a pellet made of an acrylic resin alone, wereextruded by different extruders, and were laminated inside a die, sothat a diffusing sheet with a thickness of 2 mm having a two-layerstructure including a 0.1 mm-thick diffusing layer and a 1.9 mm-thicktransparent layer was formed. Parallel light was projected to thediffusing sheet so that a luminance distribution of diffused light wasmeasured. Consequently, characteristics described below were detected.An angle a described below is an angle from the normal direction thatexpresses a direction in which the luminance declines to ½ of aluminance measured in the normal direction, and likewise γ is an anglefrom the normal direction that expresses a direction in which theluminance declines to {fraction (1/10)} of the same:

[0255] α: 16°

[0256] γ: 38°

[0257] Values αi and γi obtained by converting the foregoing into anin-medium angle are:

[0258] αi: 11°

[0259] γi: 24°

[0260] The foregoing diffusing sheet and lenticular lens film werelaminated with a 0.3 mm-thick transparent sheet made of a transparentmaterial with a refractive index of 1.5 being interposed therebetween,using a 0.025 mm-thick adhesive, so that a laminated lenticular lenssheet was formed. An adhesion surface of the lenticular lens film wasthe light-exiting surface on which the black stripes were provided. Anadhesive surface of the diffusing sheet was a surface on adiffusing-layer-provided side.

[0261] In the foregoing configuration, a distance t1 between thelight-exiting surface of the lenticular lens film as the focal plane ofthe lenticular lens array and a light-projected-side surface of thediffusing layer was 0.35 mm, which was sufficiently greater than f1=0.14mm (2.5 times).

[0262] Furthermore, a distance t2 from the focal plane to animage-observed-side surface of the diffusing layer was 0.45 mm. A beamequivalent width Db derived from this value and the aforementioned P1and f1 was:

Db=t 2×P 1/f 1=0.48 mm

[0263] which was sufficiently smaller than the pixel pitch Pg=0.96 mm(i.e., one-half).

[0264] As shown in FIG. 11, a Fresnel lens sheet matched with the focaldistance of the projection system was provided at an image-formed planeof the projection system, and the laminated lenticular lens sheet wasprovided on an image-observed side of the Fresnel lens sheet, so that animage was observed. As a Fresnel lens sheet, a transparent onecontaining no diffusing material in its base was used (with a haze valueof not more than 3%).

[0265] Consequently, excellent suppression of scintillation and a highresolving power were achieved.

Example 2

[0266] A diffusing sheet having characteristics described below wasproduced through the same process as described above concerning Example1, by decreasing the mix proportion of the light diffusing particles.Thicknesses of the diffusing layer and the transparent layer were 0.1 mmand 1.9 mm, respectively, as in Example 1.

[0267] α=9°

[0268] γ=20°

[0269] Values αi and γi obtained by converting the foregoing into anin-medium angle are:

[0270] αi: 6°

[0271] γi: 13°

[0272] The foregoing diffusing sheet and lenticular lens film werelaminated with a 1 mm-thick acryl sheet being interposed therebetween,using a 0.025 mm-thick adhesive as in Example 1, so that a laminatedlenticular lens sheet was formed.

[0273] In the foregoing configuration, a distance t1 between thelight-exiting surface of the lenticular lens film as the focal plane ofthe lenticular lens array and a light-projected-side surface of thediffusing layer was 1.05 mm, which was sufficiently greater than f1=0.14mm (not less than 7 times).

[0274] Furthermore, a distance t2 from the focal plane to theimage-observed-side surface of the diffusing layer was 1.15 mm. Amaximum signal pitch Pγ such that a degree of modulation derived fromthe foregoing value of the distance t2 and the aforementioned γi was notless than 0.75 was:

Pγ=2×t 2×tan(γi)=0.53 mm

[0275] which was sufficiently smaller than the pixel pitch Pg=0.96 mm(about one-half).

[0276] This laminated lenticular lens sheet and a transparent Fresnellens sheet, as in Example 1, were combined, and an image was observed byutilizing the aforementioned projection system. Consequently, excellentsuppression of scintillation and a high resolving power were achieved.

Comparative Example 1

[0277] The same diffusing sheet as that was used in Example 1 waslaminated directly on the lenticular lens film without providing atransparent sheet therebetween, utilizing an adhesive material, so thata laminated sheet was produced.

[0278] In the foregoing configuration, a distance t1 between thelight-exiting surface of the lenticular lens film as the focal plane ofthe lenticular lens array and a light-projected-side surface of thediffusing layer was 0.025 mm, which was significantly smaller thanf1=0.14 mm described above.

[0279] Furthermore, a distance t2 from the focal plane to animage-observed-side surface of the diffusing layer was 0.125 mm. A beamequivalent width Db derived from this value and the aforementioned P1and f1 was:

Db=t 2×P 1/f 1=0.13 mm

[0280] which was sufficiently smaller than the pixel pitch Pg=0.96 mm.

[0281] This laminated sheet and a transparent Fresnel lens sheet, as inExamples 1 and 2, were combined, and an image was observed by utilizingthe aforementioned projection system. Consequently, a sufficientresolving power was obtained, while extremely intense scintillation wasobserved and a low-quality image was obtained.

Comparative Example 2

[0282] The same image observation was carried out utilizing acombination of the same laminated lenticular lens sheet as that used inComparative Example 1 and the Fresnel lens sheet in whose base adiffusing material was dispersed, and the projection system describedabove. A haze value, an index often used for quantifying a relativelyslight diffusivity, of the base material of this Fresnel lens sheet wasapproximately 50%.

[0283] First of all, the observation was carried out in a state in whichthe Fresnel lens sheet and the laminated lenticular lens sheet weretightly close to each other. Though an effect in reducing scintillationwas observed, still more intense scintillation was observed as comparedwith Examples 1 and 2. In this state, a sufficient-level resolving powerwas obtained.

[0284] Next, the observation was carried out in a state in which theFresnel lens sheet and the laminated lenticular lens sheet were providedwith a gap of 3 mm. Such a gap can be produced when the temperature andthe moisture change. In this state, scintillation was reduced to asubstantially undetectable level, but the resolving power obviously wasimpaired and a blurry image was obtained.

[0285] Furthermore, a luminance of the projected light upon exiting was92% of that in the case where the transparent Fresnel lens sheet as inExamples 1 and 2 and comparative example 1 was used, which means that atransmission loss of 8% was confirmed.

Comparative Example 3

[0286] The diffusing sheet used in Example 1 was made to adhere to alenticular lens film by the same means so that the diffusing layer ofthe diffusing sheet came to the image-observed side, so that a laminatedlenticular lens sheet was produced.

[0287] In the foregoing configuration, a distance t1 between thelight-exiting surface of the lenticular lens film as the focal plane ofthe lenticular lens array and a light-projected-side surface of thediffusing layer was 1.925 mm, which was significantly greater thanf1=0.14 mm described above.

[0288] Furthermore, a distance t2 from the focal plane to animage-observed-side surface of the diffusing layer was 2.025 mm. A beamequivalent width Db derived from this value and the aforementioned P1and f1 was:

Db=t 2×P 1/f 1=2.2 mm

[0289] which was greater than the pixel pitch Pg=0.96 mm.

[0290] This laminated lenticular lens sheet and a transparent Fresnellens sheet, as in Examples 1 and 2 and Comparative Example 1, werecombined, and an image was observed by utilizing the aforementionedprojection system. Consequently, scintillation was reduced to asubstantially undetectable level, but the resolving power obviously wasimpaired and a blurry image was obtained.

[0291] Set conditions and evaluation results of the Examples andComparative Examples described above are shown in Table 2. Table 3explains criteria of ∘, Δ, x given as to judgment conditions andevaluation results shown in Table 2. TABLE 2 Examples ComparativeExamples Mark Unit 1 2 1 2 3 Setting Pixel Pitch on Screen Pg mm 0.960.96 0.96 0.96 0.96 Lenticular Lens Pitch Pl mm 0.15 0.15 0.15 0.15 0.15Distance from Valley to Focal Plane of fl mm 0.14 0.14 0.14 0.14 0.14Lenticular Lens Array Distance from Focal Plane to t1 mm 0.35 1.05 0.0250.025 1.925 Light-Projected-Side Surface of Diffusing Layer Distancefrom Focal Plane to t2 mm 0.45 1.15 0.125 0.125 2.025Image-Observed-Side Surface of Diffusing Layer Diffusion Angle γ deg 3820 38 38 38 (Luminance Declining to {fraction (1/10)}) Refractive Indexof Transparent Medium n — 1.5 1.5 1.5 1.5 1.5 In-Medium Equivalent Angleγi deg 24 13 24 24 24 Fresnel Lens Base Material Haze Value h % <3 <3 <350 <3 Performance Index (1) fl mm 0.15 0.15 0.15 0.15 0.15 Indices Index(2) fl × Pg/Pl mm 0.90 0.90 0.90 0.90 0.90 Index (3) Pg/2/tan(γi) mm1.07 2.05 1.07 1.07 1.07 Judgment Condition (1) t1 > fl — ◯ ◯ X X ◯Conditions Condition (2) t2 < fl × Pg/Pl — ◯ X ◯ ◯ X Condition (3) t2 <Pg/tan(γi) — ◯ ◯ ◯ ◯ X Evaluation Scintillation — ◯ ◯ X Δ ◯ ResultsResolving Power Lenti/Fresnel Tightly Close — ◯ ◯ ◯ ◯ X Lenti/Fresnelwith Gap of 3 mm — ◯ ◯ ◯ X X

[0292] TABLE 3 Judgment Conditions O Condition satisfied x Condition notsatisfied Evaluation Scintillation O Detectable limit or lower Results ΔReduced as compared with x but insufficient x Intense, resulting inlow-quality image Resolving O Not inferior to front-projection-typePower x Inferior to front-projection-type

[0293] The invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A rear-projection screen, comprising at least alenticular lens sheet and a Fresnel lens sheet, wherein the lenticularlens sheet comprises, in a base material thereof made of a resin, lightdiffusing microparticles made of a resin having a refractive indexdifferent from a refractive index of the base material, wherein thelight diffusing microparticles satisfy Formula I-1 below: 0.5 μm≦ΔN 1×d1≦0.9 μm  Formula I-1 where ΔN1 represents a difference between arefractive index of the light diffusing microparticles and a refractiveindex of the base material of the lenticular lens sheet, and d1represents an average particle diameter of the light diffusingmicroparticles.
 2. A rear-projection screen, comprising at least a lightdiffusing sheet, a lenticular lens sheet, and a Fresnel lens sheet,wherein the light diffusing sheet comprises, in a base material thereofmade of a resin, light diffusing microparticles made of a resin having arefractive index different from a refractive index of the base material,wherein the light diffusing microparticles satisfy Formula I-2 below:0.5 μm≦ΔNp×dp≦0.9 μm  Formula I-2 where ΔNp represents a differencebetween a refractive index of the light diffusing microparticles and arefractive index of the base material of the light diffusing sheet, anddp represents an average particle diameter of the light diffusingmicroparticles.
 3. The rear-projection screen according to claim 1 or 2,wherein a refractive index n1 and an Abbe constant ν1 of the materialforming the light diffusing microparticles and a refractive index n2 andan Abbe constant ν2 of the base material in which the light diffusingmicroparticles are dispersed satisfy Formula I-3 below: (n 1−n2)×(ν1−ν2)<0  Formula I-3
 4. The rear-projection screen according toclaim 1, wherein: the Fresnel lens sheet comprises, in a base materialthereof made of a resin, light diffusing microparticles made of a resinhaving a refractive index different from a refractive index of the basematerial; diffusion of light caused by the light diffusingmicroparticles contained in the Fresnel lens sheet is smaller thandiffusion of light caused by the light diffusing microparticlescontained in the lenticular lens sheet; and the light diffusingmicroparticles contained in the Fresnel lens sheet satisfy Formula I-4below: 0.1 μm≦ΔNf×df≦0.3 μm  Formula I-4 where ΔNf represents adifference between a refractive index of the light diffusingmicroparticles contained in the Fresnel lens sheet and a refractiveindex of the base material of the Fresnel lens sheet, and df representsan average particle diameter of the light diffusing microparticlescontained in the Fresnel lens sheet.
 5. The rear-projection screenaccording to claim 2, wherein: the Fresnel lens sheet comprises, in abase material thereof made of a resin, light diffusing microparticlesmade of a resin having a refractive index different from a refractiveindex of the base material; diffusion of light caused by the lightdiffusing microparticles contained in the Fresnel lens sheet is smallerthan diffusion of light caused by the light diffusing microparticlescontained in the lenticular lens sheet; and the light diffusingmicroparticles contained in the Fresnel lens sheet satisfy Formula I-4below: 0.1 μm≦ΔNf×df≦0.3 μm  Formula I-4 where ΔNf represents adifference between a refractive index of the light diffusingmicroparticles contained in the Fresnel lens sheet and a refractiveindex of the base material of the Fresnel lens sheet, and df representsan average particle diameter of the light diffusing microparticlescontained in the Fresnel lens sheet.
 6. The rear-projection screenaccording to claim 1, wherein: the lenticular lens sheet contains thelight diffusing microparticles satisfying Formula I-1 as a maindiffusing element, and further contains, as a sub diffusing element,light diffusing microparticles that are made of a resin having arefractive index different from that of the base material of thelenticular lens sheet and that satisfy Formula I-5 below: 0.1μm≦ΔNs×ds≦0.3 μm  Formula I-5 where ΔNs represents a difference betweena refractive index of the light diffusing microparticles serving as thesub diffusing element and a refractive index of the base materialcontaining the same, and ds represents an average particle diameter ofthe light diffusing microparticles serving as the sub diffusing element.7. The rear-projection screen according to claim 2, wherein the lightdiffusing sheet contains the light diffusing microparticles satisfyingFormula I-2 as a main diffusing element, and further contains, as a subdiffusing element, light diffusing microparticles that are made of aresin having a refractive index different from that of the base materialof the light diffusing sheet and that satisfy Formula I-5 below: 0.1μm≦ΔNs×ds≦0.3 μm  Formula I-5 where ΔNs represents a difference betweena refractive index of the light diffusing microparticles serving as thesub diffusing element and a refractive index of the base materialcontaining the same, and ds represents an average particle diameter ofthe light diffusing microparticles serving as the sub diffusing element.8. The rear-projection screen according to claim 6 or 7, wherein anaverage particle diameter dm and a mix proportion by volume Am of thelight diffusing microparticles as the main diffusing element, athickness tm of a layer of the base material containing the lightdiffusing microparticles as the main diffusing element, a difference ΔNmbetween a refractive index of the light diffusing microparticles as themain diffusing element and a refractive index of the base materialcontaining the light diffusing microparticles as the main diffusingelement, an average particle diameter ds and a mix proportion by volumeAs of the light diffusing microparticles as the sub diffusing element, athickness ts of a layer of the base material containing the lightdiffusing microparticles as the sub diffusing element, a difference ΔNsbetween a refractive index of the light diffusing microparticles as thesub diffusing element and a refractive index of the base materialcontaining the light diffusing microparticles as the sub diffusingelement are set so as to satisfy Formula I-6 below:Am×tm/dm×ΔNm>As×ts/ds×ΔNs  Formula I-6
 9. The rear-projection screenaccording to claim 1 or 2, wherein a lenticular lens array whoselengthwise direction is directed in a horizontal direction is providedon a light-projected-side surface of the Fresnel lens sheet.
 10. Arear-projection screen, comprising a lenticular lens sheet and a Fresnellens sheet, wherein the lenticular lens sheet and the Fresnel lens sheetcomprise, in base materials thereof made of resins, light diffusingmicroparticles made of resins having refractive indices different fromthose of the base materials, respectively; wherein: diffusion of lightcaused by the light diffusing microparticles contained in the Fresnellens sheet is smaller than diffusion of light caused by the lightdiffusing microparticles contained in the lenticular lens sheet; and thelight diffusing microparticles contained in the Fresnel lens sheetsatisfy Formula I-4 below: 0.1 μm≦ΔNf×df≦0.3 μm  Formula I-4 where ΔNfrepresents a difference between a refractive index of the lightdiffusing microparticles contained in the Fresnel lens sheet and arefractive index of the base material of the Fresnel lens sheet, and dfrepresents an average particle diameter of the light diffusingmicroparticles contained in the Fresnel lens sheet.
 11. Arear-projection screen, comprising at least a light diffusing sheet, alenticular lens sheet, and a Fresnel lens sheet, wherein the lightdiffusing sheet and the Fresnel lens sheet comprise, in base materialsthereof made of resins, light diffusing microparticles made of resinshaving refractive indices different from those of the base materials,respectively; wherein: diffusion of light caused by the light diffusingmicroparticles contained in the Fresnel lens sheet is smaller thandiffusion of light caused by the light diffusing microparticlescontained in the light diffusing sheet; and the light diffusingmicroparticles contained in the Fresnel lens sheet satisfy Formula I-4below: 0.1 μm≦ΔNf×df≦0.3 μm  Formula I-4 where ΔNf represents adifference between a refractive index of the light diffusingmicroparticles contained in the Fresnel lens sheet and a refractiveindex of the base material of the Fresnel lens sheet, and df representsan average particle diameter of the light diffusing microparticlescontained in the Fresnel lens sheet.
 12. A rear-projection displaycomprising a rear-projection screen according to any one of claims 1, 2,10, and
 11. 13. A rear-projection display comprising a spatialmodulation element, and a rear-projection screen on whose surface on alight-projected side an image formed by the spatial modulation elementis projected so that the image is observed from an image-observed sideopposite to the light-projected side, wherein the rear-projection screenincludes a first screen element for converting projected light from thespatial modulation element into substantially parallel light, and asecond screen element for diffusing the substantially parallel light,wherein the second screen element includes a lenticular lens array thatis provided on the surface on the light-projected side and whoselengthwise direction is directed in a vertical direction, a diffusinglayer provided at the image-observed side of the lenticular lens array,and a transparent layer provided between the lenticular lens array andthe diffusing layer, wherein a distance t1 between alight-projected-side surface of the diffusing layer and a focal plane ofthe lenticular lens array satisfies Formula II-1 below, and a distancet2 between an image-observed-side surface of the diffusing layer and thefocal plane of the lenticular lens array satisfies Formula II-2 below: t1≧f 1  Formula II-1t 2≦f 1×Pg/P 1  Formula II-2 where f1 represents adistance between a valley of the lenticular lens array and the focalplane, Pg represents a pixel pitch on the screen, and P1 represents anarray pitch of the lenticular lens array.
 14. A rear-projection displaycomprising a spatial modulation element, and a rear-projection screen onwhose surface on a light-projected side an image formed by the spatialmodulation element is projected so that the image is observed from animage-observed side opposite to the light-projected side, wherein therear-projection screen includes a first screen element for convertingprojected light from the spatial modulation element into substantiallyparallel light, and a second screen element for diffusing thesubstantially parallel light, wherein the second screen element includesa lenticular lens array that is provided on the surface on thelight-projected side and whose length-wise direction is directed in avertical direction, a diffusing layer provided at the image-observedside of the lenticular lens array, and a transparent layer providedbetween the lenticular lens array and the diffusing layer, wherein adistance t1 between a light-projected-side surface of the diffusinglayer and a focal plane of the lenticular lens array satisfies FormulaII-1 below, and a distance t2 between an image-observed-side surface ofthe diffusing layer and the focal plane of the lenticular lens arraysatisfies Formula II-3 below: t 1≧f 1  Formula II-1t2≦Pg/2/tan(γi)  Formula II-3 where f1 represents a distance between avalley of the lenticular lens array and the focal plane, Pg represents apixel pitch on the screen, and γi represents an in-layer equivalentangle in the transparent layer that is obtained by converting anobservation angle γ at which a luminance of {fraction (1/10)} of that ina normal direction is obtained due to diffusion caused by the diffusinglayer, and is expressed as Formula II-4 below: γi=asin(sin(γ)/n)  Formula II-4 where n represents a refractive index n ofthe transparent layer.
 15. The rear-projection display according toclaim 13 or 14, wherein the first screen element is a Fresnel lens sheetmade of a transparent material containing substantially no diffusingmaterial.
 16. The rear-projection display according to claim 13 or 14,wherein a light absorbing layer is provided on a light non-transmissionportion in a vicinity of the focal plane of the lenticular lens array ofthe second screen element.
 17. A rear-projection screen on whose surfaceon a light-projected side an image formed by a spatial modulationelement is projected so that the image is observed from animage-observed side opposite to the light-projected side, therear-projection screen comprising: a first screen element for convertingprojected light from the spatial modulation element into substantiallyparallel light; and a second screen element for diffusing thesubstantially parallel light, wherein the second screen element includesa lenticular lens array that is provided on the surface on thelight-projected side and whose length-wise direction is directed in avertical direction, a diffusing layer provided at the image-observedside of the lenticular lens array, and a transparent layer providedbetween the lenticular lens array and the diffusing layer, wherein adistance t1 between a light-projected-side surface of the diffusinglayer and a focal plane of the lenticular lens array satisfies FormulaII-1 below, and a distance t2 between an image-observed-side surface ofthe diffusing layer and the focal plane of the lenticular lens arraysatisfies Formula II-5 below: t 1≧f 1  Formula II-1t 2≦f 1×P1×0.7  Formula II-5  where: f1 represents a distance between a valley ofthe lenticular lens array and the focal plane, and P1 represents anarray pitch of the lenticular lens array; and a unit of t1 is accordingto that of f1, and a unit of t2 is millimeters.
 18. A rear-projectionscreen on whose surface on a light-projected side an image formed by aspatial modulation element is projected so that the image is observedfrom an image-observed side opposite to the light-projected side, therear-projection screen comprising: a first screen element for convertingprojected light from the spatial modulation element into substantiallyparallel light; and a second screen element for diffusing thesubstantially parallel light, wherein the second screen element includesa lenticular lens array that is provided on the surface on thelight-projected side and whose length-wise direction is directed in avertical direction, a diffusing layer provided at the image-observedside of the lenticular lens array, and a transparent layer providedbetween the lenticular lens array and the diffusing layer, wherein adistance t1 between a light-projected-side surface of the diffusinglayer and a focal plane of the lenticular lens array satisfies FormulaII-1 below, and a distance t2 between an image-observed-side surface ofthe diffusing layer and the focal plane of the lenticular lens arraysatisfies Formula II-6 below: t 1≧f 1  Formula II-1t2≦0.35/tan(γi)  Formula II-6  where: f1 represents a distance between avalley of the lenticular lens array and the focal plane, and γirepresents an in-layer equivalent angle in the transparent layer that isobtained by converting an observation angle γ at which a luminance of{fraction (1/10)} of that in a normal direction is obtained due todiffusion caused by the diffusing layer, and is expressed as FormulaII-7 below: γi=a sin(sin(γ)/n)  Formula II-7  where: n represents arefractive index n of the transparent layer; and a unit of t1 isaccording to that of f1, and a unit of t2 is millimeters.
 19. Therear-projection screen according to claim 17 or 18, wherein the firstscreen element is a Fresnel lens sheet made of a transparent materialcontaining substantially no diffusing material.
 20. The rear-projectionscreen according to claim 17 or 18, wherein a light absorbing layer isprovided on a light non-transmission portion in a vicinity of the focalplane of the lenticular lens array of the second screen element.